Brand Z's annual sales are affected by the sales of related products X and Y as follows: Each$1 millionincrease in sales ofBrand Xcauses a$2.6milliondecline in sales ofBrand Z,whereas each$1 millionincrease in sales ofBrand Yresults in an increase of$0.3millionin sales ofBrand Z.Currently,Brands X,Y, and Z are each selling$6 millionper year. Model the sales ofBrand Zusing a linear function. (Letz= annualsales ofZ(in millions of dollars),x= annualsales ofX(in millions of dollars), andy= annualsales ofY(in millions of dollars).)

z=?