The total number of children's ticket bought is 28 - x
The total cost of adult's ticket is $30x.
The total cost of children's ticket is 420 - 15x.
The total cost of the tickets is 420 - 15x.
The total number of children's ticket = total ticket - adult ticket
28 - x
Cost of the adult's ticket = cost per ticket x total ticket bought
$30x
Cost of the children's ticket = cost per ticket x total ticket bought
$15 x (28 - x) = $420 - 15x
Total amount spent = $420 - 15x + 30x = $420 - 15x
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