Rewrite 125y3 as (5y)3.
Since both terms are perfect cubes, factor using the sum of cubes formula, a3+b3=(a+b)(a2-ab+b2) where a=z and b=5y.
Rewrite using the commutative property of multiplication.
Multiply -1 by 5.
Apply the product rule to 5y.
Raise 5 to the power of 2.