first of al, i'm new here in this forum so i really, really expect that people here would help me overcome my weakness in trigonometry. so here's my question:

a tower & a monument stand on a level plane. the angle of depression of the top & bottom of the monument varied from the top of the tower are 13degrees & 31degrees respectively; the height of the tower is 145 ft. find the height of the monument.

pls make an illustration of this problem so that i could understand more how to solve this problem.