Answer:
The final position is 5 feet below the back of the truck
Step-by-step explanation:
* Lets explain how to solve the problem
- A crane lifts a pallet of concrete blocks 8 feet from the back of
 a truck
- The crane lowers the pallet 13 feet after the truck drives away
- Assume that the zero level of the position of the ballet of concrete
 blocks is the back of the truck
∵ The crane lifts the pallet of concrete blocks 8 feet from the back
 of the truck
- That means it take the pallet from zero to 8
∴ The height of the pallet of concrete blocks is 8 feet over
  the starting position
∵ The crane lowers the pallet of concrete blocks 13 feet
- That means the crane lower the pallet from the height 8 and
 lift it down 13 feet, so we must to take out from the 8 feet the
 13 feet to find the final position of the pallet of concrete blocks
∴ The pallet position is ⇒ 8 - 13 = -5
∴ The position of the pallet of concrete blocks is 5 feet below the
  starting position which is the back of the truck
* The final position is 5 feet below the back of the truck
