Why do you have to add all the time

Someone answer this asap rn for ! a discount store’s prices are 25% lower than department store prices. the function c(x) = 0.75x can be used to determine the cost c, in dollars, of an item, where x is the department store price, in dollars. if the item has not sold in one month, the discount store takes an additional 20% off the discounted price and an additional $5 off the total purchase. the function d(y) = 0.80y - 5 can be used to find d, the cost, in dollars, of an item that has not been sold for a month, where y is the discount store price, in dollars. create a function d(c(x)) that represents the final price of an item when a costumer buys an item that has been in the discount store for a month. d(c(x)) =

Credit card a offers an introductory apr of 3.4% for the first three months and standard apr of 15.7% thereafter,

Solve for x in the equation x2 - 12x + 36 = 90. x= 6+3x/10 x=6+2/7 x= 12+3/22 x = 12+3/10