The total repair cost for each store is the cost of repairs added to the sales tax. The amount of money saved will be the difference between the two total costs.
Gratuity of $180 I would multiply the actual repair cost without including tax to determine the gratuity. So just multiply $1200 by 0.15 getting $180. As an suggestion, calculating 15% in your head is actually quite simple. What you do is calculate 10%, divide that in half, then add together. So for the $1200 example, you have 1200/10 = 120 half of 120 is 60 120 + 60 = 180 So you have a top of $180.
A = P (1 + r/n)^(nt) where A is the amount in the account, P is the principle, r is the interest rate , n is the times compounded per year, t is the number of years
