First we want to isolate x from 5x + y = 9 so to do so. We subtract y from both sides. 5x + y - y = 9 - y Simplify. 5x = 9 - y Divide both sides by 5. 5x/5 = 9/5 - y/5 Simplify again. x = 9 - 5/y Substitute x = 9 - 5/y So 10 * 9 - 5/y - 7y = -18. We wanna isolate y so... 10 * 9 - 5/y Multiply the fractions. (9 - y) * 10/5 Divide the numbers (10/5 = 2) 2(-y + 9) Now we want to expand this. 2 * 9 + 2(-y) Apply the minusplus rule 2 * 9 - 2y This gives us 18 - 2y From there we can add the similar elements -2y - -7y = -9y 18 - 9y = -18 Subtract 18 from both sides. 18 - 9y - 18 = -18 - 18 Simplify again. -9y = -36 Now divide both sides by -9 -9y/-9 = -36/-9 This gives us y = 4. For x we just want to substitute 4 into it. So 9 - 4/5 which is 5/5 which translates to 1. Therefore y = 4 and x = 1.
