Answer: Isaac used 40 blocks in all.
Step-by-step explanation:
The first stack was 5 blocks tall. The second stack was 9 blocks taller than the first. This means that the number of blocks in the second stack is 5 + 9 = 14 blocks
The third stack was 6 blocks shorter than the second stack. This means that the number of blocks in the third stack is 13 - 6 = 7 blocks
The last stack was 7 blocks taller than the third stack. This means that the number of blocks in the last stack is 7 + 7 = 14 blocks
The total number of blocks that Isaac used would be
5 + 14 + 7 + 14 = 40 blocks
