Both car meet at one point and they started from opposite ends so Total distance travel by both car = 200 miles

Lets say distance travel by car from Cincinnati to Toledo is D1 and speed of that car is X mph

that makes speed of that car traveling from Toledo to Cincinnati X+15 mph , lets say it cover distance D2 in 1 hour and 36 mins.

so we now have D1+D2 = 200 miles

and

D1 = x *1.6 (distance = speed * time)

D2= (x+15) *1.6

so we have x*1.6 + (x+15)*1.6 = 200 ---> (x+x+15) *1.6 = 200

I hope now this will help you understand

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