What’s is the answer help me out here

Can someone me with this problem i don't understand i need

In which form is the following function written? y = - 2(x – 3)(x + 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