var formulas = new Array()
formulas["ff1"] = "15.3 * num_one + 679";
formulas["ff2"] = "11.6 * num_one + 879"
formulas["n1"] = "14.7 * num_one +496";
formulas["n2"] = "8.7 * num_one + 829";

function getCheckedNum()
{
var selected;
for(var loop=0;loop<window.document.convert.csopi.length;loop++)
{
if(window.document.convert.csopi[loop].checked == true)
{
selected = loop;
}
}
return selected;
}
function calculate(num_one)
{
if((isNaN(parseInt(num_one))))
{

return;
}
var selected_index = getCheckedNum();
var selected_value = window.document.convert.csopi[selected_index].value;


formula = formulas[selected_value];
var answer = eval(formula);
alert(answer);
}