First let's find the profit for each t-shirt, by subtracting the selling price and the buying price:

So they have a profit of $17.5 per t-shirt sold.
Now, to find the number of t-shirts they have to sell to break even, we just need to divide the right cost of $740 by the profit value of one t-shirt:

So they need to sell approximately 43 t-shirts to break even.