Answer:
9h² + 42hk + 49k²
Explanation:
Given
(3h + 7k)²
= (3h + 7k)(3h + 7k)
Each term in the second factor is multiplied by each term in the first factor, that is
3h(3h + 7k) + 7k(3h + 7k) ← distribute both parenthesis
= 9h² + 21hk + 21hk + 49k² ← collect like terms
= 9h² + 42hk + 49k²