Let Xavier's favourite fraction be a/b, Yessie's favourite fraction = b/a and Zorro's favourite fraction = c/d,
c/d x a/b = 12/35 . . . . . . . . (1)
c/d x b/a = 15/7 . . . . . . . . (2)
(1) x (2) = c/d x a/b x c/d x b/a = 12/35 x 15/7
c^2 / d^2 = 36/49
c^2 = 36
c = 6
d^2 = 49
d = 7
Xaviers favourite fraction = 12/35 / 6/7 = 2/5
Yessies favourite fraction = 5/2
Zorro favourite fraction = 6/7
Number of cars washed by the eight teams per hour = 2 * 8 = 16 cars.
Number of cars washed by the eight teams in 5 = 16 * 5 = 80 cars.
The teams should charge $600/80 = $7.50
I used a math calculator to evaluate this expression you just plug it in and it gives you the answer with all the steps. use the app FX math junior, but this is the answer ; 2419/720=3.3597