How to subrtact a negative from a negative?

Can anyone me with 32,33,36,37,and 40.

45 was divided by a power of ten to get 4.5. what power of ten was it divided by? people 4.5

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