text: Q: Roger has 5 tennis balls. He buys 2 more cans of 
  tennis balls. Each can has 3 tennis balls. How many 
  tennis balls does he have now?
  A: Roger started with 5 balls. 2 cans of 3 tennis balls 
  each is 6 tennis balls. 5 + 6 = 11. The answer is 11.
  Q: The cafeteria had 23 apples. If they used 20 to 
  make lunch and bought 6 more, how many apples 
  do they have?