The nine Ring Wraiths want to fly from Barad-Dur to Rivendell. Rivendell is directly north of Barad-Dur. The Dark Tower reports that the wind is coming from the west at 54 miles per hour. In order to travel in a straight line, the Ring Wraiths decide to head northwest. At what speed should they fly (omit units)

76.37 mph

Explanation:

The speed of wind is 54 miles per hour.

-Northwest direction forms a 45°. The west constituent needs to cancel out the 54mph.

-From this we notice that the west and northwest are the isosceles sides of a right triangle, we therefore use the Pythagorean Theorem to find the speed of the 3rd constituent(Hypotenuse):

Hence, they have to fly at 76.37 mph

d. air pressure decreases as altitude increases.