Question 662372
1.)  Work backward.  7 * 5 = 35 - 10 = 25 is the number
Proof:25 + 10 = 35/5 = 7
2.)  Work backward.  15-10 = 5*5 = 25
Proof:25 / 5 = 5 + 10 = 15
3.)  x/3 = 30 so, multiply both sides by 3 and x = 90
4.) 15*2 = 30+7=37-8=29
5.) Work backward.  20+15=35/5=7*3=21-12=9
Proof: 9+12=21/3=7*5=35-15=20
6.) x is the number of cars: (x - 1/2x)-1/4(x - 1/2x) = 15
x - 1/2x - 1/4x + 1/8x = 15
8/8x - 4/8x - 2/8x + 1/8x = 15
3/8x = 15
x = 40 cars
7.) 1/2(1/2x - 15) - 15 = 75
1/4x - 15/2 - 15 = 75
1/4x - 15/2 - 30/2 = 75
1/4x - 45/2 = 75
1/4x = 75 + 45/2
1/4x = 150/2 + 45/2
1/4x = 195/2
x = 195/2(4)
x=$390 starting with
Proof = 390(1/2)=195-15=180(1/2)90-15=75
Proof:  (1/2)40=20 by Milo. 40-20=20,(1/4)20=5 by Ken 20-5=15 by Vernon
8.)x+6-9=0 so x-3=0 so x=3rd floor
Proof: 3 + 6 = 9 - 9 = 0