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
(20:4)x3=15 (Ellas grade)
(20:5)x4=16 (Minhs grade)
X / 6/7 is 3 2/5. First, concert the numbers to decimals for simplicity sake, and you get x/.857 = 3.4. Multiply both sides by .857 to get x alone and you get x ≈ 2.9143