Question 202855
1)  x+y=120,,,,,x=120-y
2)  (1/2)x +(3/4)y=80
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subst  (1)  into  (2)
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(120-y)/2 + (3/4)y =80
60-y/2 +(3/4)y =80
y/4 = 20
y=80,,,,,,x=120-80=40
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check (1)  40 + 80 = 120,,,ok
(2) 40/2 + (3/4) 80 = 20 + 60 = 80,,,,ok