How do you prove this If you add (a+b) to both sides, you can use inverse, commutative, and associative laws to show that both sides are equal and...

How do you prove this If you add (a+b) to both sides, you can use inverse, commutative, and associative laws to show that both sides are equal and then use the cancellation law to finish the proof.

The goal is to prove -(a+b)=(-a)+(-b) this is Lemma 2.3.2(4)

But I need to solve it using methods above