Need help in js

Tell us what’s happening:
ok so i have noclue what im doing wrong here somone help … also annyonewho has time to tech please let me help them

Your code so far

var a = 3;
var b = 17;
var c = 12;

// Only modify code below this line
var a += 0;
var b += 0;
var c += 0;

a = a + 12;
b = 9 + b;
c = c + 7;

Your browser information:

Your Browser User Agent is: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36.

Link to the challenge:

Re-read the description.

You do not need to redeclare the variables a, b and c because they are already declared in the first three lines.
You have to refactor the last three lines in the alternative format. If you look at the example, two ways to add a value to a variable are:
myVar = myVar + 5;
myVar += 5;

Thank You very new at this only day 4