Solve by using the strategies for solving application problems. It costs a manufacturer $9.99 to produce sunglasses that sell for $34.99. How many pairs of sunglasses must the manufacturer sell to make a profit of $18,125? Step 1 This real-world problem can be solved using a linear equation. Let x be the number of pairs of sunglasses. The sell price of one pair is $34.99. The revenue generated after selling x pairs is, therefore, Revenue = x dollars. It costs the manufacturer $9.99 to produce one pair of sunglasses. The total cost of producing x pairs is, therefore, Cost= x dollars.