Compound Assignment help needed

Tell us what’s happening:
can any one please assist on this problem? I assign variables a, b, c to with operator but still code is not working.

Your code so far

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

// Only modify code below this line

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

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Link to the challenge:

Look at the challenge instructions again. You are supposed to be using the += operator. Remember, that when I write x = x + 2, that I can use the += operator to accomplish the same thing with x += 2