Aradio telescope has a parabolic dish. radio signals are collected at the focal point(focus) of the parabola. the distance from the vertex of the parabolic dish to the focus is 20 feet. the vertex of the dish is located at a point 30 feet above the ground and 80 feet to the east of a computer that reads and records data from the telescope. the diameter of the dish is 120 feet. what is the depth of the parabolic dish?