Anyone know how to solve this? ? i’m terrible at fractions

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

Credit card a offers an introductory apr of 3.4% for the first three months and standard apr of 15.7% thereafter,

What is the greatest number of parts of a circle that can be formed by cutting the circle with 7 straight cuts? (note: the parts do not have to be equal in size)