Solve the given problems. Sketch an appropriate figure, unless the figure is given.
An antenna was on the top of the World Trade Center (before it was destroyed in 2001 ). From a point on the river 7800 ft from the Center, the angles of elevation of the top and bottom of the antenna were $12.1^{\circ}$ and $9.9^{\circ},$ respectively. How tall was the antenna? (Disregard the small part of the antenna near the base that could not be seen.) The former World Trade Center is shown in Fig. 4.61