So, im t trying to find the original price and sale price of a book for example and the amount of discount is 2.80 dollars and the percent paid was 60 percent and percent saved was 40 %, plz i just need the explanation of how to do it cause i got more of these problems

Frank has a devised a formula for his catering business that calculates the number of meatballs he needs to prepare. the formula is m=4a+2c, where c=number of children; m=number of meatballs; a=number of adults. how many meatballs are required for a party of 10 adults and 5 children?