you want to take away the y’s in each equation so you are left with the x’s for now
2(11x - y = 21) = 22x - 2y = 42
you are going add both equations to get:
31x = 31
x = 1
now substitute 1 into one equation
(9*1) + 2y = -11
9 + 2y = -11
2y = -20
y = -10
x = 1
y = -10
