Respuesta :

hbj

Answer:

(15, -6)

Step-by-step explanation:

x + y = 9

x - y = 21

x = 9 - y

plug in x into second equation

9 - y - y = 21

9 - 2y = 21

-2y = 12

y = -6

plug in y.

x - (-6) = 21

x + 6 = 21

x = 15

check

15 + (-6) = 9

15 - (-6) = 21