Question

How to use (3+a+b)3 to a commutative law of multiplication to a equivalent equation

Answer 1

first off, you have no equation -- just an expression (as you might expect, an equation needs an equal sign: =)

The only commutative parts I can see here are

(3+a+b)3 = 3(3+a+b)

now, if you want to talk about commutative addition, or distributive properties, then we can go on a bit further.