GMAT Studs....Can someone explain this questions. I am completely lost. Greatly appreciated!!!

A grocer stacked oranges in a pile. The bottom layer was rectangular with 3 rows of 5 oranges each. In the second layer from the bottom, each orange rested on 4 oranges from the bottom layer, and in the third layer, each orange rested on 4 oranges from the second layer. Which of the following is the maximum number of oranges that could have been in the third layer?

o 5
o 4
o 3
o 2
o 1