Can you give me some step-by-step instructions for this math problem: Tom decides to buy some shirts from his favorite fandoms because there is a sale on his favorite website.  He buys 5 t-shirts from each of his 4 favorite fandoms.  The shirts normally cost $15 each but there is a 20% off sale.   The order qualified for free shipping but he still needed to pay 10% tax.  How much did he pay?