If the sum of two numbers is 27 and the difference is 11

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

4+(2+x) can you me solve this problem

1) prove that 731^3−631^3 is divisible by 100 2) prove that 99^3−74^3 is divisible by 25