Arturo O. answered 05/10/20
Experienced Physics Teacher for Physics Tutoring
You can factor "a" from the numerator and b2 from the denominator.
... = 4a(a2 - b2) / [3b2(a + b)]
Note that
a2 - b2 = (a - b)(a + b)
So now you have
... = 4a(a - b)(a + b) / [3b2(a + b)] = 4a(a - b) / (3b2)
This is as far as you can simplify.