Try This Tough ACT Math Question

This question is a variation of one of the toughest questions in the New ACT book:

A coach assigns a uniform to each of her 18 players, each with a different number from 1 to 18. She tells the players to split up into pairs, with the condition that the sum of the pair’s numbers equals a perfect square. Once all the players pair up in a way that meets the coach’s condition, which player will be paired with player number 3?
A). 1
B). 4
C.) 6
D.) 9
E.) 13