ada yg bisa jawab ngak?tolong dibantu ya :) makasih

1) x - y = 4
2x + y = 8
---------------(+)
3x = 12
x = 4
disubstitusi ke pers :
x - y = 4
4 - y = 4
- y = 4 - 4
y = 0
hp = { 4,0} ( D )

2) 2x + 3y = 15 |×2
4x - y = - 19
maka
4x + 6y = 30
4x - y = - 19
------------------(-)
7y = 49
y = 7
disubstitusi ke pers :
2x + 3y = 15
2x + 3(7) = 15
2x + 21 = 15
2x = 15 - 21
2x = - 6
x = - 3
hp = { - 3 , 7 } ( B )

3) 3x + y = - 1 |×3
x + 3y = 5
maka
9x + 3y = - 3
x + 3y = 5
--------------------(-)
8x = - 8
x = - 1
disubstitusi ke pers
3x + y = - 1
3(-1) + y = - 1
- 3 + y = - 1
y = - 1 + 3
y = 2
a = x = - 1
b = y = 2
nilai 3a + 3b = 3(-1) + 3(2) = - 3 + 6 = 3 ( C )

5) x = 5
y - 3x - 12 = 0
y - 3(5) - 12 = 0
y - 15 - 12 = 0
y - 27 = 0
y = 27
hp = ( 5 , 27 ) ( D )