Will give find (4.8 x 106)(3.6 x 103) (2 x 105) , expressed in scientific notation.  a) 8.64 x 104  b) 8.64 x 106  c) 8.64 x 108   d) 17.28 x 104

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