Ans!!
Your question is incomplete as you have not mention what is to be find out.
So, if your question is:
A man on the top of a vertical tower observes a car moving at a uniform speed coming directly towards it . if it takes 12 min for the angle of depression to change from 30degree to 45degree , how soon after this will the car reach the observer tower
Then the solution is as follows:
Let AB be the vertical tower and P and Q be the position of the car at the angle of depression 30° and 45°.
Let AB = h and
PQ = x
Then
∠APB = 30° and ∠AQB = 45°
Now
In Δ ABQ,
tan 45° =
⇒BQ = h
In Δ APB
tan 30° =
Hence, the time to reach the tower =16.39 minutes.