At a zoo, ratio of king penguins to emperor penguins is 2 : 3. In all, there are 45 king and emperor penguins combined. How many emperor penguins are at the zoo? Explain how to solve this problem in two ways: with the aid of a strip diagram and with the aid of a ratio table. In each case, discuss the reasoning involved in the method; in other words, explain why the method makes sense.