Question

Which ordered pair is the solution to the system of equations?

{x+y=−1
{3x−y=21

A. (5.5, −6.5)

B. (7, −8)

C. (10, −11)

D. (5, −6)

Answer 1

x+y=-1
3x-y=21
add them equations

x+y=-1
3x-y=21 +
4x+0y=20

4x=20
divide by 4
x=5

x+y=-1
5+y=-1
minus 5 both sides
y=-6

(x,y)
(5,-6)

D is answer