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
