-3x+7y=-16 (a)
-9x+5y=16 (b)
First, multiply (a) by -3, and then add both equations to eliminate x:
9x-21y = 48
+
-9x+ 5y=16
_________
-16y = 64
Solve for y
y= 64/-16
y= -4 (c)
replace (c) in (a)
-3x+7y=-16 (a)
-3x+7(-4)=-16
Solve for x
-3x-28 =-16
-3x=-16+28
-3x= 12
x=12/-3
x= -4