Let f(x)=-5x+3 and g(x)=6x-2. find f •g and it's domain.

For this case what you should do is the composition of functions.
 f • g = f (g (x)) = - 5 (6x-2) +3
 Rewriting the function we have
 f (g (x)) = - 30x + 13
 Then, the domain of the function will be that for which the function is defined. In this case, the function is defined for all reals, or equivalently:
 x = (- inf, inf)
 answer
 f (g (x)) = - 30x + 13
 x = (- inf, inf)

Aline graph should be used

The answer is 225 miles per 4.5 hours. hope this ; )