A cheetah running 90 feet per second is 100 feet behind a gazelle that is running 70 feet per second. How long will long will it take the cheetah to catch up to the gazelle.

Let t be the time taken by cheetah to catch up to the gazelle.

In t sec  cheetah run 90t feet.

In t sec gazelle run 70t feet.

90t-100 =70t.

90y-70t=100.

20t=100.

t=100/20

=5 sec.

After 5 seconds  cheetah  catch up to the gazelle.