Answer: k = 15
Explanation:
60 times some number k must be a perfect square.
Factor 60 to see which values do not have a pair:
60 = 2 · 2 · 3 · 5 --> 60 = 2 · 2 · 3 · 5
↓
3 · 5 are not pairs
So, you need to multiply 60 by 15 to make a perfect square
60 × 15 = 900 →
