When you substitute, you should solve one equation for a variable. I'll solve the first equation for r.
r + 2s = 30 Subtract 2s from both sides
r = -2s + 30
Now, substitute the r-value into the second equation and solve for s.
2r - s = -45 Substitute in the r-value
2( -2s + 30 ) - s = -45 Use the distributive property
-4s + 60 - s = -45 Combine like terms
-5s + 60 = -45 Subtract 60 from both sides
-5s = -105 Divide both sides by -5
s = 21
Now, plug the s-value into the first equation.
r + 2s = 30 Substitute in the s-value
r + 2(21) = 30 Multiply
r + 42 = 30 Subtract 42 from both sides
r = -12
So, s = 21 and r = -12.