Answer:
x+y=85 and x-y=20
x=85-y x=20+y
85-y=20+y
85-20-y-y=0
65-2y
-2y=65
y=-65/-2
y=32.5
finding x by substituting y=32.5
x+y=85
x+32.5=85
x=85-32.5
x=52.5
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