I am horrible at algebra its just not made for me to understand

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax

What are the excluded values? m+5/mn+3m

Which radical expression is a rational number? a. √ 360 b. √ 644 c. √ 225 d. √ 122