Final answer:
The expression for the cost of items Lamar intends to buy before tax is 24.99s + 38.99p, representing the total cost of shirts and pants.
Step-by-step explanation:
The expression representing the cost of the items Lamar wants to buy before tax is simply the sum of the cost of shirts and pants without the sales tax included, which is calculated by multiplying the number of shirts (s) by the cost of each shirt ($24.99) and the number of pants (p) by the cost of each pair of pants ($38.99). The expression is 24.99s + 38.99p.