We can relate the attendance to the ticket price as a=mx+c where m and c are to be found.
When x=10 a=30000 and when x=9 a=33000.
Plugging these values in we get 30000=10x+c and 33000=9x+c, so if we subtract these two equations from one another we eliminate c: x=-3000. Now we can calculate c: 30000=-30000+c, so c=60000 and a=60000-3000x. We have related attendance to the ticket price.
R(x)=ax.
Now we can relate the revenue to the ticket price: (a) R(x)=60000x-3000x².
(b) R(x)=-3000(x²-20x+100-100)=-3000(x-10)²+300000. When x=$10 R(x) is maximum.
(c) R(x)=0 when 3000x=60000, so x=$20 (and attendance is zero).