1.
x + y = 5 ⇒ x = 5 - y
2(5 - y) - y = 7 (substitute)
10 - 2y - y = 7 (distribute)
10 - 3y = 7
-3y = -3 (subtraction)
y = 1(divide)
x + (1) = 5 (substitute then solve)
x = 4
2.
–4x – 6(–2x + 6) = 4 (substitute)
–4x + 12x – 36 = 4 (solve)
8x –36 = 4
8x = 40
x = 5
y = –2(5) + 6
y = –10 + 6
y = –4
3.
3x + y = 7 ⇒ y = 7 - 3x
-7x - 5(7 - 3x) = 25
-7x - 35 + 15x = 25
8x - 35 = 25
8x = 60
x = 7.5
y = 7 - 3(7.5)
y = 7 - 22.5
y = 15.5
4.
x + 3y = 9 ⇒ x = 9 - 3y
2(9 - 3y) + 4y = 7
18 - 6y + 4y = 7
- 2y + 18 = 7
- 2y = -11
y = 5.5
x = 9 - 3(5.5)
x = 9 - 16.5
x = - 7.5
