This is a simple way that immediately comes to my mind
1. Create a base class that will be used by all the 3 pages
public class BasePage : System.Web.UI.Page
{
public int YourMethod(string str)
{
int someNum = 1;
return someNum;
}
}
2. All your 3 pages should inherit this, instead of System.Web.UI.Page
public class Default : BasePage
{
protected void Page_Load(object sender, EventArgs e)
{
}
}
Hope this helps! Comment if you have any questions.