9 (r - s) + 5 (2r - 2s)

9 (r - s) + 5 (2r - 2s) = 0

perform distributive multiplication

9 (r) + 9 (-s) + 5 (2r) + 5 (-2s) = 0

9r - 9s + 10r - 10s = 0

9r + 10r - 9s - 10s = 0

19r - 19s = 0

19r = 19s

r = 19s/19

r = s

Ok this isn't as bad as it looks. all you have to do is multiply the terms in the parentheses by the terms outside of them. so it would b 9 x (r-s) + 5 x (2r - 2s).

You would then get (9r-9s) + (10r-10s). Remove the parentheses and combine like terms. 9r + 10r is 19r and - 9s plus - 10s is - 19s. so the answer is 19r - 19s.