Hello from MrBillDoesMath!
Answer:
x = -3, y = 0
Discussion:
5x + 5y = -15 =>
x + y = -3 => (divide both sides by 5)
x + y - y = -3 -y => (subtract y from both sides)
x = -3 - y
Substitute x = -3 - y into the top equation:
-3x - 5y = -9 =>
-3(-3-y) - 5y = 9 => ( substitute -3 -y for x)
(-3)(-3) + (-3)(-y) - 5y = 9 =>
9 + 3y - 5y = 9 => ( -*- is a + number)
9 -2y = 9 =>
9 - 9 -2y = 9 - 9 => (subtract 9 from both sides)
-2y = 0 =>
y = 0
Since x = -3 -y, x = -3 - 0 = =3
Regards,
MrB
P.S. I'll be on vacation from Friday, Dec 22 to Jan 2, 2019. Have a Great New Year!