Solve with substitutiion: r + 2s = 30 and 2r - s = - 45

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.