Answer:
boys + girls = 45 -------(1)
There boys 17 more than girls, boys = girls + 17 ----------(2)
substitute (2) in (1)
girls + 17 + girls = 45
2 x girls + 17 = 45
2 x girls = 45 - 17
2 x girls = 28
girls = 14
substitute in (2): boys = girls + 17 = 14 + 17 = 31
option D