The number of adults that are there will be 368 adults.
Let adults = a
Let children = c
The equation to solve the question will be:
a + c = 865 ....... i
30a + 9c = 15513 ...... ii
From equation i, c = 865 - a
Since 30a + 9c = 15513
30a + 9(865 - a) = 15513
30a + 7785 - 9a = 15513
30a - 9a = 15513 - 7785
21a = 7728
a = 7728/21
a = 368
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