23−(−9). PLease help me

Which expression can be used to determine the slope of the line that passes through the points -6, three and one, -9

Determine the difference: 3.2 × 1010 – 1.1 × 1010. write your answer in scientific notation.

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