60 mph is 60*1.5=<<60*1.5=90>>90 feet per second.
40 mph is 40*1.5=<<40*1.5=60>>60 feet per second.
Thus, for every second, the cheetah advances on the gazelle by 90-60=<<90-60=30>>30 feet per second.
To close on a distance of 200 feet, it would take the cheetah 210/30=7 seconds to catch the gazelle.
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