9x+4y=12 --------------(1)
x+4y=18 ------------------(2)
(1)-(2)⇒ 9x+4y=12
(-) x+4y=18
------------------------
9x-x+4y-4y=12-18
8x=-6
dividedby 8 each side
(8x/8)=(-6/8)
x=(-2*3)/(2*4)
x=-3/4
there fore x= -3/4
x value substuting in equation (2)
(2)⇒x+4y=18
(-3/4)+4y=18
adding (3/4) in each side
(-3/4)+4y+3/4=18+3/4
4y=(72+3)/4 LCM 1,4 is 4
4y=75/4
dividedby 4 each side
4y/4=(75/4)/4
y=75/16
there fore x= -3/4 , y=75/16