Answer:
100+y = 3x.......(1)
4x + y=180.......(2)
making y the subject
y= 180-4x.........(3)
putting equation 3 into equation 1 we have
100+(180-4x)=3x
100+180-4x=3x
280=3x+4x
280=7x
divide both sides by 7
40=x
putting x=40 into equation 2 we have
4(40)+y=180
160+y=180
y=180-160
y=20
