How Do I Create A Script That Calculates The Number Of Textbox Filled With Value

function myFunction() {
        var y = document.getElementById("subject1ca").value;
        var z = document.getElementById("subject1exam").value;
        var x = +y + +z;
        document.getElementById("total1").value = x;
}
function myFunction2() {
        var y = document.getElementById("subject2ca").value;
        var z = document.getElementById("subject2exam").value;
        var x = +y + +z;
        document.getElementById("total2").value = x;
}
function myFunction3() {
        var y = document.getElementById("subject3ca").value;
        var z = document.getElementById("subject3exam").value;
        var x = +y + +z;
        document.getElementById("total3").value = x;
}
function myFunction4() {
        var y = document.getElementById("subject4ca").value;
        var z = document.getElementById("subject4exam").value;
        var x = +y + +z;
        document.getElementById("total4").value = x;
}
function myFunction5() {
        var y = document.getElementById("subject5ca").value;
        var z = document.getElementById("subject5exam").value;
        var x = +y + +z;
        document.getElementById("total5").value = x;
}
function myFunction6() {
        var y = document.getElementById("subject6ca").value;
        var z = document.getElementById("subject6exam").value;
        var x = +y + +z;
        document.getElementById("total6").value = x;
}
function myFunction7() {
        var y = document.getElementById("subject7ca").value;
        var z = document.getElementById("subject7exam").value;
        var x = +y + +z;
        document.getElementById("total7").value = x;
}
function myFunction8() {
        var a = document.getElementById("total1").value;
        var b = document.getElementById("total2").value;
        var c = document.getElementById("total3").value;
        var d = document.getElementById("total4").value;
        var e = document.getElementById("total5").value;
        var f = document.getElementById("total6").value;
        var g = document.getElementById("total7").value;
        var h = +a + +b + +c + +d + +e + +f + +g;
        document.getElementById("total8").value = h;
}