Buses run every 9 min starting at 6:00 A. M. You get to the bus stop at 7:16 A. M. How long will you wait for a bus?

You can simply do something like this:

6; 00

6:09

6:18

etc

Or you could estimate by doing 9x8=72, and 72 minutes past 6:00 is 7:12, plus 9 more minutes would be 7:21 and that is when the next bus comes. 21-16=5 so the answer would be 5 minutes