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The Colliding Ferrari and Mercedes problem:
A Ferrari is heading south at a constant speed on Broadway (a north/south street)
at the same time a Mercedes is heading west on Aloha Avenue (an east/west street).
The Ferrari is 624 feet north of the intersection of Broadway and Aloha,
at the same time that the Mercedes is 400 feet east of the intersection.
Assume the Mercedes is traveling at the constant speed of 32 miles/hour.
Find the speed of the Ferrari so that a collision occurs in the intersection of Broadway and Aloha.
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The Mercedes speed 32 miles per hour is 
= 46.933 feet per second.
The Mercedes travel time is 
= 
= 8.523 seconds (rounded).
The Ferrari speed should provide the same time, so the Ferrari speed must be
= 73.214 feet per second, or 
= 49.92 miles per hour. ANSWER
Solved.
Alternatively, you can write a proportion
= 
and find the answer from there x = 
= 49.92 miles per hour,
the same number.
The proportion expresses the fact that the two travel times are equal.
It does not matter that in the proportion different terms are in different units,
because the corresponding terms in the proportion have consistent units.
Solved in two ways for your better understanding and thoroughly explained.
