3(a + b) and 3a + b - NOT EQUIVALENT because
3(a + b) = 3a + 3b
used distributive property a(b + c) = ab + ac
4(x + 2y) and 8y + 4x - EQUIVALENT because
4(x + 2y) = (4)(x) + (4)(2y) = 4x + 8y = 8y + 4x
used distributive property a(b + c) = ab + ac
and commutative property a + b = b + a