Ulangang Matematika (Sistem Persamaan Linear Dua Variabel) #Mohon Bantuan.nya?

1.
1/2x-y=-7 |2|
2/2x-2y=-14
x-2y=-14

1/3x+1/2y=0 |3|
x+3/2y=0 |2|
2x+3y=0

x-2y=-14 |3| 3x-6y=-42
2x+3y=0 |2| 4x+6y=0
__________+
7x =-42
x =-6
x di substitusi
2x+3y=0
-12+3y=0
3y=12
y=4

x-y
-6-4=-10

cuma ngerti nomor 1 nih sisanya lupa udah lama gk ngerjain soal kyk gni...
maaf ya....