Answer:
The height of  the hill is 45 feet .
Step-by-step explanation:
Refer the attached figure 
Let AB be the height of hill 
We are given that He determines that the angle of elevation to the top of the hill is 50°
So, 
Now  He then walks 40  feet farther from the base from the hill and determines that the angle of elevation to the top of the hill is now 30°
So, CD=40 feet
BD=BC+CD=BC+40

In ΔACB 

In ΔADB

So,equate 1 and 2

Substitute the value in equation 1
1.1917 (37.59)=AB
44.796=AB
Hence the height of  the hill is 45 feet .