An airplane flying at an altitude of 10,000 feet passes directly over a fixed object on the ground.
One minute later, the angle of depression of the object is 42°.
Approximate the speed of the airplane to the nearest mile per hour.
Ans: 126 mi/hr
Is this right so far? . . . . no
Your set-up is correct, but . . .
* - - - - - *
| 42° *
10,000 | *
The plane flew: . feet in one minute.
It would fly: . feet in one hour.
It would fly: . miles in one hour.
Therefore, its speed is about 126 mph.