If you would like to know how many of each type of ticket were sold, you can calculate this using the following two equations:
a ... the number of drakes fan club tickets
s ... the number of no members tickets
$550 = a * $20 + s * $25 ... 550 = 20 * a + 25 * s
a + s = 25 ... a = 25 - s
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550 = 20 * a + 25 * s
550 = 20 * (25 - s) + 25 * s
550 = 20 * 25 - 20 * s + 25 * s
550 - 20 * 25 = 5 * s
550 - 500 = 5 * s /5
s = 50 / 5
s = 10 tickets
a = 25 - s = 25 - 10 = 15 tickets
Result: There were 15 drakes fan club and 10 no members tickets sold.