Answer:
x = 5, y = 4
Step-by-step explanation:
x + 4y = 21
4x - 16 = y
x + 4(4x - 16) = 21
x + (16x - 64) = 21
(17x - 64) = 21
17x = 85
x = 85/17
x = 5
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x + 4y = 21
5 + 4y = 21
4y + 5 = 21
4y = 16
y = 16/4
y = 4
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