math

var question = document.getElementById("question").innerHTML;
var f = question[0]+question[1];
if (question[2] == "-") {var radnja = question[2];}
if (question[2] == "+") {var radnja = question[2];}
if (question[4] != "=") {var s = question[3]+question[4];} else { var s = question[3]; }
var rezultat = eval(f+radnja+s);
var gotovo = question+rezultat;
document.getElementById("answer").value=rezultat;