Question

R/3 = 7

Answer 1

R=21. 21/3=7. To check your answer, you can do 7x3 and it'll equal 21.

Answer 2

Are you just trying to isolate the r?

If so.... r/3 = 7
Multiply 3 on both sides to clear the denominator
3(r/3) = 7(3)
3 = 21

CHECK
21/3 = 7