Let's call the prices a and c, a for adult...
The cost of an adult ticket is £7 more than the cost of a child ticket:
a = 7 + c
The total cost of the six tickets is £86.
86 = 2a + 4c
c = a-7
86 = 2a + 4(a-7) = 6a - 28
114 = 6a
a = 19
Answer: £19
Check:
That implies c=12.
2a+4c = 2(19)+4(12) = 38 + 48 = 86, good
common ratio = a4/a3 = a3/a2
8/a3 = a3/18
(a3)^2 = 8 * 18
(a3)^2 = 144
a3 = 12 or a3 = -12
common ratio = 8/12 or common ratio = 8/(-12)
common ratio = 2/3 or common ratio = -2/3
Answer: 12 or -12
You can sort them on the shapes that are the same or different
