Note that the third column is the square numbers.
A 4 layer solid pyramid has 4 square layers.
The six layer pyramid on the left is solid. See how many fewer blocks there are on the one on the right?
A six layer solid pyramid could be used to make 3 hollow pyramids.
Solid 6 on left, hollow 6, hollow 4, and a 2 layer
A 10 layer solid pyramid could be used to make 5 hollow pyramids.
The bottom layer has 100 blocks. How many blocks are in the entire pyramid?
Complete the entire spread sheet and figure out how many fewer blocks would be in a hollow pyramid.