a=adult tickets
s = senior tickets
a+s=465 a = 465-s
23a + 13s = 7145
substitute in a = 465-a
23 (465-s) + 13s = 7145
distrubute
10695 - 23s +13s =7145
combine like terms
10695 - 10s = 7145
subtract 10695 from each side
-10s = -3550
divide by -10
s = 355
senior tickets sold 355
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