a = adult ticket price
s = student ticket price
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7a + 2s = 87
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4a + 6s = 74
4a = 74 - 6s
a = 74/4 - (6/4)s
a = 37/2 - (3/2)s
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7a + 2s = 87
7(37/2 - (3/2)s) + 2s = 87
7(37/2) - 7(3/2)s + 2s = 87
(259/2) - (21/2)s + 2s = 87
(21/2)s - 2s = (259/2) - 87
(21/2)s - (4/2)s = 259/2 - 174/2
(17/2)s = 85/2
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s = 85/2(2/17)
s = 85/17
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Answer:
s = $5
a = $11
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