A pilot flying an altitude of 11790m sees a mountain 12450m high. What is direct distance between the plane and the mountain? Show working.?

Refer to the diagram below.

In ΔPMA:

PM² = PA² + MA² (Pythagorean theorem)

PM² = (2900 m)² + (12450 - 11790 m)²

PM = 2974 m

Distance between the plane and the mountain = 2974 m

This is one of those fun ones. You need one more piece of information if you are asking for direct distance and that would be the angle above or below the plane's horizon where the mountain appears. Without that, the question has not single solution.

not enough info to answer this.

provide the complete question, not part of it.