Problem Solving

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

I'm getting 3.

Let 1 be the oranges in the first layer, 2 be the oranges in the second
layer and 3 be the oranges in the third layer

For the first 2 layers, we get

1 1 1 1 1
_2 2 2 2
1 1 1 1 1
_2 2 2 2
1 1 1 1 1

2nd and 3rd layer, we get

2 2 2 2
_3 3 3
2 2 2 2

Hence only 3 oranges can be in the 3rd layer.

Thanks again!