How to get a number to display in alert box rather than NAN

Question

I am learning javascript and I made a simple program to convert feet to meters and lbs to kg and I want to display the output using alert boxes in the correct measurements

I checked the variables using typeof and its coming back number but the alert boxes are still saying NAN.

I am new to javascript and Im following along with a udemy course.

var kgMark = parseFloat(kgMark); 
var meterMark = parseFloat(meterMark);
var bmiMark = parseFloat(bmiMark);
var feetMark = parseFloat(feetMark);
var lbsMark = parseFloat(lbsMark);

kgMark = lbsMark / 2.2046;
meterMark = feetMark / 3.2808;
bmiMark = kgMark / (meterMark * meterMark);

feetMark = prompt('How tall is mark in feet?');
lbsMark = prompt('How much does mark weigh in pounds?');



alert('Mark is ' + ' ' + kgMark + ' '+ 'kilograms');
alert('Mark is ' + ' ' + meterMark + ' ' + 'meters');
alert('Marks BMI is ' + ' ' + bmiMark);

I have tried it several different ways and I am truly stuck. I keep getting the NAN error in the alert box.

Answer 1

First take a value then perform every logic:

var feetMark = prompt('How tall is mark in feet?');
var lbsMark = prompt('How much does mark weigh in pounds?');


feetMark = parseFloat(feetMark);
lbsMark = parseFloat(lbsMark);

var kgMark = lbsMark / 2.2046;
var meterMark = feetMark / 3.2808;
var bmiMark = kgMark / (meterMark * meterMark);

alert('Mark is ' + ' ' + kgMark + ' '+ 'kilograms');
alert('Mark is ' + ' ' + meterMark + ' ' + 'meters');
alert('Marks BMI is ' + ' ' + bmiMark);