beserta rumus,untuk no. 15-16

15.
x - 2y = 10
3x + 2y = - 2
------------------ (+)
4x = 8
x = 8/4
x = 2

x - 2y = 10
2 - 2y = 10
-2y = 10-2
-2y = 8
y = 8/-2
y = -4

Hp = { 2, -4 }