Set 40 = 5x + 10
Subtract 10 on both sides, then divide 30 by 5
x = 6
Your answer should be C. 3x^3√2
4" x 2500 ft², namely 4 ft x 2500 ft², will just be 4*2500*ft*ft², or 10000 ft³.

since there are 27 ft³ in 1 yd³, then how many yd³ are there in 10000 ft³?
10000/27, that many yd³.
Girls: 81
boys: 75
4x +6 = 156
4x = 150
x = 37.5
2x = 75
girls: 75 + 6
boys: x