Modular Program : Error, won't call modules

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication19
{
    class Program
    {
        public static void Main()
        {
            string name = "";
            int itemQuantity = 0;
            double itemPrice = 0.0;
            string state = "";
            double total = 0.0;

            name = PromptAndInput("Enter the name of the customer: ");
            state = PromptAndInput("In which state (NY / NJ / FL) ? ");

            if (state != "NJ" & state != "nj" & state != "NY" & state != "ny" & state != "FL" & state != "fl")
            {
                Console.WriteLine("Error");
                while (state != "NJ" & state != "nj" & state != "NY" & state != "ny" & state != "FL" & state != "fl")
                {
                    state = PromptAndInput("In which state (NY / NJ / FL) ? ");
                }
            }

            itemQuantity = int.Parse(PromptAndInput("How many items were purchased?: "));
            if (itemQuantity < 0)
            Console.WriteLine("Error");
            while (itemQuantity < 0)
            itemQuantity = int.Parse(PromptAndInput("How many items were purchased?: "));

            itemPrice = double.Parse(PromptAndInput("What was the unit price of the items?: "));
            if (itemPrice < 0)
            Console.WriteLine("Error");
            while (itemPrice < 0)
            itemPrice = double.Parse(PromptAndInput("What was the unit price of the items?: "));

            computeTotal(itemQuantity, itemPrice, total, name);
            computeTax(state, total, itemQuantity, itemPrice);
        }

        public static string PromptAndInput(string prompt)
        {
            string userInput;
            Console.Write(prompt);
            userInput = Console.ReadLine();
            return userInput; 
        }

        public static object computeTotal(int itemQuantity, double itemPrice, double total, string name)
        {
            total = itemQuantity * itemPrice;
            Console.WriteLine();
            Console.WriteLine("--------------------------------------------------");
            Console.WriteLine("The total sales for " + name + " are: " + total);
            return total;
        }

        public static object computeTax(string state, double total, int itemQuantity, double itemPrice)
        {
            double taxAmt = 0.0;
            double totalSales = 0.0;
            double tax = 0.0;

            total = itemQuantity * itemPrice;

            if (state == "NJ" | state == "nj")
            {
                tax = 0.07;
            }
            else if (state == "NY" | state == "ny")
            {
                tax = 0.04;
            }
            else if (state == "FL" | state == "fl")
            {
                tax = 0.06;
            }

            taxAmt = total * tax;
            totalSales = total + taxAmt;

            Console.WriteLine("The tax amount is " + taxAmt + " based on a tax rate of: " + tax);
            Console.WriteLine("The total with taxes is: " + totalSales);
            Console.WriteLine("--------------------------------------------------");
            return totalSales;
        }
    }
}