From the top of a 200 meters high building, the angle of depression to the bottom of a second building is 20 degrees. from the same point, the angle of elevation to the top of the second building is 10 degrees. calculate the height of the second building.

It says that the buildings together are 200 meters high and from the top pf the first to bottom of the second is 20(whole building) but from the top of the first to second is 10 (half of the building ) so if the degree if half the high will be half too so the high will be 200/2 = 100 meters high for each buildings :))
i hope this is helpful 
have a nice day 

Tan(20o) = 200 / L 

L = 200 / tan(20o) 

tan(10o) = H2 / L 

H2 = L * tan(10o) 

= 200 * tan(10o) / tan(20o) 

Height of second building = 200 + 200 * tan(10o) / tan(20o)