Denise and Donna want to exchange secrets from across a crowded whispering gallery. Recall that a whispering gallery is a room which, in cross section, is half of an ellipse. If the room is 30 feet high at the center and 90 feet wide at the floor, how far from the outer wall should each of them stand so that they will be positioned at the foci of the ellipse? Fill in the blank: Denise and Donna should each stand ft from the outer wall so that they will be positioned at the foci of the ellipse. Round your answer to the nearest whole ft (no decimal places).