Final answer:
To break even, you need to sell at least 53 shirts.
Step-by-step explanation:
To break even with the cost of the printing machine, we need to calculate the total cost and the profit from selling each shirt. The total cost is the cost of the machine plus the cost to make each shirt. In this case, the total cost is $450 + $21 = $471 per shirt. The profit from selling each shirt is the selling price minus the cost to make each shirt. In this case, the profit is $30 - $21 = $9 per shirt. To break even, we need to divide the total cost by the profit per shirt: $471 / $9 = 52.33. Since we can't sell a partial shirt, we need to round up to the nearest whole number. So, we need to sell at least 53 shirts to break even.