Describe how to use a ten fact to find the difference for 15-8

This is pretty simple if you learn how! All you really need to do is round.

15 is closest to 20,
and 8 is closest to 10.

You could also round down.

10, and 8.

10 - 8 = 2, and with your extra five, 5 + 2 = 7

A) for the n row: 22+(n-1)×6therefore,b) 100-22=78that means (n-1)×6=7878÷6=1313+1=1414th row has 100 seats