To solve this problem you must apply the proccedure shown below:
1- Let's calculate the total cost of 4 t-shirts at Bixbys, by multiplying this quantity by one t-shirt costs ($11.80):

3- You know that you can buy 5 t-shirts at Baxter’s for the same price that you can buy 4 t-shirts at Bixbys. Therefore, to calculate the cost of one t-shirt at Baxter’s, you need to divide the total cost obtained above by 5 t-shirts:

The answer is: $9.44