My question is this A car travels 504 miles at a certain spe

My question is this. A car travels 504 miles at a certain speed. If the speed had been 14 mi faster the trip could have been made in 3 hours less time. Find the speed. I tried writing it as T=D/R
t-3=504/x-14 but i cant seem to get teh answer please help me understand how to get to the answer. Im taking an online math class and it doesnt really have sources to help me, im not in the state of the college to be able to go to a tutor center.

Solution

t = 504 / r

t - 3 = 504 / r+14

substituting ___ 504/r - 3 = 504 / r+14

multiplying by r(r+14) ___ 504r + 7056 - 3r^2 - 42r = 504r

subtracting 504r and dividing by -3 ___ r^2 + 14r - 2352 = 0

factoring ___ (r + 56)(r - 42) = 0

r - 42 = 0 ___ r = 42