In a certain city, the daily use of water [in hundreds of gallons) per household can be modelled with the pdfx) = 0.15e'0'15xforx 2 U. 3] Find the probability that a household chosen at random will use at most 40E:- gallons per day. (Hint: f0-15e'15xdx = E_D'15X + C} b] Find the probability of using more than 400 gallons per day c) Find d such that the probability of a randomly chosen household using up to d hundreds of gallons of water is 0.8