Tolong pake banget ini mahhh:((((( pake cara yaaa plis bantuin ok?

3/4a - 1/3b = 2 >> dikali 1/2
1/2a + 2/3b = 4 >> dikali 3/4

3/8a - 1/6b = 1
3/8a + 1/2b = 3
---------------------- (-)
-4/6b = -2
b= 3

3/4a - 1/3b = 2
3/4a - 1 = 2
3/4a = 3
a = 4

a-3b = 4- 3(3) = 4-9 = -5 (B)