The faster car is travelling at 160 laps/hr, so in t=3/40 hr, it will have travelled 12 laps, not 9. I think you just mislabelled the units---you meant to say 9 miles, maybe?
Hey Rosemary -- here's the "play-by-play": PRETEND "A" is 1 mile behind ... at 10 mph closing speed, one mile needs 1/10 of an hour to close ... 120 mph covers 240 "half-miles"/hr OR 480 "qtr-miles"/hr ... three (3) of these "qtr-miles" would be covered
160 times/hr ... 1/10 of an hr travels 16 laps when 1 mile behind ==> the 3/4 mile lag would take 12 laps to catch up ... Best wishes, ma'am :)
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