if x^2-y^2=72 and y-x=6, then x+y=

Question

the choices:

a)-12

b)-6

c)-3

d)3

e)12

Answer 1

x² - y² = 72

(x - y)(x + y) = 72

-(y - x)(x + y) = 72

-6(x + y) = 72

x + y = -12