A 4fttall fence runs parallel to the wall of a house at a distance of 10 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 is 20 ft high and the horizontal ground extends 20 ft from the fence. The length of the shortest ladder is D ft. (Round the final answer to the nearest tenth as needed. Round all intermediate values to the nearest thousandth as needed.)