If Sarah wanted to include a 15 percent gratuity, based on the total cost of the computer repair , excluding shipping , how would you find her new total cost ?

C is the cost BEFORE gratuity
i would divide C by 20 because then i’d be left with 5% of C
20 x 5 = 100%
then i would multiply the 5% of C by 3 to get 15% of C
the you would add C and the 15% of C together to get the total cost

What can we do about it