Attendance is 27,000 for $11 ticket, and attendance is 31,000 for $8 ticket.
If attendance is linearly related to ticket price, for a ($11-$8=) $3 drop in ticket price there is a (31,000-27,000=) 4,000 attendance rise, which means (4,000/$3~=) 1,333 attendance rise per dollar decrease.
So we can formulize their relation (A=attendance, P=price, C=constant)
P = -(3/4000)A + C
if we put the values for $11 ticket
11 = -(3/4,000)*27,000 + C
C = 11 + 81/4 = 31.25
so the A-P relation formula is
P = 31.25 - (3/4000)A
or
A = -(4000/3)*(P - 31.25)
The revenue(R) is
R = A*P = -(4000/3)*(P- 31.25)*P = -(16000/3)*(4P2 - 125P)
we need max(R)
so we need to find the P value for which the derivative of R equals to zero
R' = -(16000/3)*(8P - 125) = 0 => P = 125/8 = 15.625
For maximum revenue, ticket price has to be $15.63