Question

Use the substitution method to solve the system of equations. Choose the

correct ordered pair.
y= 10x - 9
y = x + 18
A. (1,1)
B. (2,11)
C. (3,21)
D. (4, 31)

Answer 1

C. (3,21)

Explanation:

multiply the 2nd equation by -10 to cancel out the x.

y = 10x - 9

-10(y = x + 18)

y = 10x - 9

-10y = -10x - 180

-9y = -189

y = 21

Now plug y = 21 into either original equation.

y = x + 18

21 = x + 18

Take 18 from each side.

3 = x

Answer: (3, 21)

Answer 2

Answer: C. (3,21) - x= 3 ; y= 21

Explanation:

y= 10x - 9 .(-1)

y = x + 18

-y= -10x + 9

y = x + 18

-9x + 27

x= 27

-9

x= 3

y = x + 18

y= 3 + 18

y= 21