An 8-ft-tall fence runs parallel to a wall of a house at a distance of 30 ft. Find the length of the shortest ladder that extends from the ground to the house without touching the fence. Assume the vertical wall of the house and the horizontal ground have infinite extent. Let L be the length of the ladder, x be the distance from the base of the ladder to the fence, d be the distance from the fence to the house and h be the distance from the ground to the point the ladder touches the house. What is the objective function, in terms of x?