Question 250081
We are dealing with three dimensional space and we need to first calculate the ground distance from the point on the below the aircraft to the tower (which is the hypotenuse of the ground triangle with legs 10 and 15) This is also the other leg of the triangle with one leg 4  and the distance from the aircraft to the tower is the hypotenuse
Let's calculate the first hypotenuse.
10^2+15^2=c^2=325
now we have the two legs squared of the other triangle.
16 and 325
16+325=c^2=341
c=18.47 km from control tower to the aircraft.
Tutor Alan combined it all.