10 adults + 5 children = $75 ------------- (1)
8 adults + 10 children = $78 ------------- (2)
(1) x 2 : 20 adults + 10 children = $150 ------------- (1a)
(1a) - (2) : 12 adults = $72
1 adult = $6
Substitute 1 adult = $6 into (1):
10 ($6) + 5 children = $75
$60 + 5 children = $75
5 children = $15
1 child = $3
Therefore 1 adult = $6 and 1 child = $3
Find 6 adult and 10 children:
6 adults + 10 children = 6(6) + 10(3) = 36 + 30 = $66
Answer: $66
