Trigonometry

[shut cobalt]

How do I solve this?
A 100 meter high mast stands on the top of a mountain.
The base and the top of the mast are seen from a
observation point P of the valley at elevation angles α = 11.3° and β = 12.4°.
How high is the top of the mountain above the observation point?

Solution is: 996,88 m

[slim shuttle]

draw it

[shut cobalt]

I did and came to this:
TAN (12,4) * d = h+100
TAN (11,3) * d = h

[shut cobalt]

dunno how to solve it.