The first thing to recognize is that you have FOUR unknowns and so need four equations. This easiest way to see this is not to use subscripts.
$x_1 = p =$ people attending during 2013.
$y_1 = q=$ average ticket price during 2013.
$x_2 = r=$ people attending during 2014.
$y_2 = s =$ average ticket price during 2014.
Now what symbols are used to represent unknowns makes no real difference, but if you are not used to subscripted symbols, this should make it very clear that you are dealing with four distinct unknowns.
So you need four equations to solve it. Using p, q, r, and s, what are those four equations? If you can't get them all, which can you get?
HINT What is the relationship between p and r? How about q and s?