Help Compound Assignment With Augmented Addition

Tell us what’s happening:
Plz explain, I didn’t understand this part. TIA

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;

Your browser information:

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Link to the challenge:

You’re going to use the compound assignment operator for adding:

// this statement:
a = a + 12;

// is the same as this one; this is what you should use for this challenge:
a += 12;

Thank you, have help me solve it.