There are 54 people playing tennis at the regional event at the same time. some are playing doubles, and some are playing singles. there are 18 matches in progress. a singles match requires 2 players, and a doubles match requires 4 players. this can be modeled with this system of equations. 2s + 4d = 54 s + d = 18 which ordered pair is the most reasonable solution to this system of equations?

(9, -9)

(-9, -9)

(-9, 9)

(9, 9)