A bank operates both a drive-up facility and a walk-up window. On a randomly selected day, let X=the proportion of time that the dive-up facility is in use (at least one customer is being served or waiting to be served) and Y= proportion of time that the walk-up window is in use. Then the set of possible values for (X,Y) is the rectangle D={(x,y):0? ? ? 1, 0? ? ? 1 Suppose the joint pdf of (X,Y) is given by:

f (x, y ) = =(x+12) 0