Question 271183
They approach at the sum, 110 mph.
110 mph = 110*5280 ft/hour
= 110*5280/3600 ft/sec
t = 500/(110*5280/3600) seconds
t =~ 3.099 seconds
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15 mph = 22 ft/sec  If you remember that, you can shorten the time needed to do a lot of problems.