tolong dibantu no 20&22 pake cara!!

20. 3/4X-1/3Y=2 (×12)
=9x-4y=24
1/2X+2/3Y=4 (×12)
=6x+8y=48
Maka,
9x-4y=24|×2|18x-8y=48
6x+8y=48|×3|18x+24y=144
=-32y=-96
=y=-96÷-32
=y=3..... nilai b
Nilai b=3 disubstisikan ke nilai 1
9x-4y=24
9x-4(3)=24
9x-12=24
9x=24+12
9x=36
X=4.... nilai a

Jadi nilai a-3b= 4-3(3)=4-9=-5(b)