Gary and his friends go to see a movie. Gary buys x movie tickets at the rate of $8 per ticket and a tub of popcorn for $5.50.  
If f(x) is the total amount he spends at the theater, which of the following linear functions models this situation? 
A.  f(x) = 8x + 5.50 
B.  f(x) = 5.50x + 8
C.  f(x) = 44x 
D.  f(x) = 13.50x