Question

3r = 10 + 5s, when r = 10

Answer 1

3(10)=10+5s
30=10+5s
20=5s
4=s

Answer 2

3r = 10 + 5s, where r = 10
Substitute 10 for r.
3(10) = 10 + 5s
30 = 10 + 5s
Subtract 10 from each side.
20 = 5s
Divide by 5.
4 = s