The general equation for profit is written below:
Profit = Revenue - Total Cost
Revenue is the total sales you get while total cost includes the capital and other variable costs.
Letting x be the number of t-shirts, the revenue would be 15x, while the total cost is (20 + 9x). So, the profit equation becomes:
150 ≤ 15x - (20 +9x)
The ≤ symbol means that the right side of the equation must be equal or greater than 150 so that you can reach your goal profit.
Solving for x,
150 + 20 ≤ 15x - 9x
x ≥ 28.33
Hence, the answer is A.
