tan x = opposite/adjacent
The adjacent side is 275. For each angle, the opposite side is its portion of the height of the tower. Add them together.
275*tan39 degrees + 275*tan25 degrees = about 351 feet
From the figure, note that the height of the window is the lower portion of the height of the tower (the window is that height above the ground) = 275*tan25 degrees = about 128 feet