1a+2b+3c=17 2a-2b+4c=20 4a+1b-4c=-3 elimination find all variables

Me answer number 3plz explain how you do it

Aschool typically sells 500 yearbooks each year for 50 dollars each. the economic calls does a project and discovers that they can sell 100 more yearbooks for every $5 decrease in price. the revenue for yearbook sales is equal to the number of yearbooks sold times the price of the yearbook. let x represent the number of $5 decrease in price. if the expression that represents the revenue is written in the form r(x)=(500+ax)(50-bx). to maximize profit, what price should the school charge for the yearbooks? what is the possible maximum revenue? if the school attains the maximum revenue, how many yearbooks will they sell?

The composite figure is made up of a parallelogram and a rectangle. find the area. a. 76 sq. units b. 48 sq. units c. 124 sq. units d. 28 sq. units