I have attached a diagram , a terrible one .. sorry bout that .
The positions of the aircraft are A and E for the first and second observations respectively . By finding AE , then you can find its speed .
Note that .
Now , use the cosine rule ,
Phythagoras theorem ,
Using , , v=196m/s
Convert this to km/h
You have got most of the information here , surely you can get the angle of descent .