Help me with this problem please?

Question

"During rush hour., Bill can drive 15 miles using the side roads in the same time that it takes to travel 10 miles on the freeway. If Bill's rate on the side roads is 8 mi/h faster than his rate on the freeway, find his rate on the side roads."

Answer 1

D=rt

15=(x+8)t
10=xt
15=xt +8t
5=8t
t=5/8 of an hour

10=x(5/8)
8/5(10)=x
16=x
24=x+8

24mph