Final answer:
Lewa's hiking backpack weighs 13 pounds.
Step-by-step explanation:
To write an expression for the weight of Lewa's backpack, we first need to determine the weight of Alani's backpack.
Since Alani's backpack weighs 36 pounds, half of that weight is 36/2 = 18 pounds.
Lewa's backpack weighs 5 pounds less than half of Alani's backpack, so we subtract 5 from the weight of Alani's backpack: 18 - 5 = 13 pounds.
Therefore, the expression to describe the weight of Lewa's backpack is 13 pounds.