Question 478450
let t be the exact time it has to reach
x/40 =t+1/6

x/40-1/6= t

x/30 =t+4/15
x/30 -4/15=t

x/40-1/6 = x/30-4/15

x/40-x/30 = -4/15+1/6

(3x-4x)/120 = (-8+5)/30

-x= 4(-3)
-x=-12
x=12 miles