What is the value of r in the equaition 1/7 (105+r) = 20

You want to make it so all of the integers are on one side and all of the variables are on the other.

So.

1/7 (105+r) = 20

Opening up the parenthesis:

1/7 * 105 + 1/7 * r = 20

15 + 1/7r = 20

-15 - 15

1/7r = 5

*7 * 7

r = 35

So r equals 35.