Final answer:
To calculate the selling price of the shirt, add the markup amount to the cost price. The markup amount is 40% of the cost price. The selling price is the sum of the markup amount and the cost price.
Step-by-step explanation:
To calculate the selling price of the shirt, we need to add the markup amount to the cost price. The markup amount is 40% of the cost price, which is calculated by multiplying the cost price ($4) by 40% (0.40). The markup amount is $1.60.
Now, to calculate the selling price, we add the markup amount to the cost price. The selling price is $4 + $1.60 = $5.60.