Question

Use substitution to solve the system of
equations: 5x + 5y = -30
2x - y = 15

Answer 1

5x + 5y = -30
Divide through by 5
X + Y = -6
Multiplying the equation by 2 and the equation 2x - y = 15 by 1 in order to get rid of x
2x + 2y = -12
2x - y = -15
Subtracting both equations
3y=3
y=1
Substituting y = 1 to get x in any equation
Using 2x - y = -15
2x - 1 = -15
2x =-15 + 1
2x = -14
x = -14/2
x = -7

Answer 2

x = 3, y = - 9

Explanation:

5x + 5y = - 30...... (1)

2x - y = 15

-y = 15 - 2x

y = 2x - 15..... (2)

From equations (1) & (2)

5x + 5(2x - 15) = - 30

5x + 10x - 75 = - 30

15x = 75 - 30

15x = 45

x = 45/15

x = 3

Plug x = 3 in equation (2)

y = 2*3 - 15

y = 6 - 15

y = - 9

Therefore,

x = 3, y = - 9

or

(x, y) = (3, - 9)