Step-by-step explanation:
Given equation are:
9(1-x)=27----(1)
x-y=-11/2----(2)
Now, solving equation (1)
9-x=27
9-27=X
-18=X
X=-18
substituting X=-18 in equation (2)
-18-y=-11/2
-36-2y=-11
-2y=36-11
-2y=25
y=-25/2
again, by question,
X+Y=-18+(-25/2) [Substituting the values of xand y]
=-18-25/2
=(-36-25)/2
=-61/2
