Use elimination to solve the system x plus 7y equals 16 and 3x - 7y equals 4?
x+7y=16 ---------------------------1
3x- 7y=4 ---------------------------2
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1+2
x+7y=16
3x-7y=4
4x=20
x=5
substitute x = 5 in x+7y=16
(5)+7y=16
7y=11
y=11/7