I am not exactly sure how to start. If someone can please help me with one of these word problems I would be extremely grateful.

An airplane is flying at an altitude of 3 miles at a rate of 400 miles per hour. Find the rate of change of angle a at the moment that the observer is standing at a horizontal distance of 4 miles from the plane,

A ladder 15 ft long is leaning against the wall of a house. The base of the ladder is pulled away from the house at a rate of 2 ft per second.Consider the triangle created by the ground the wall and the ladder. How fast is the area changing when the ladder’s top is 12 ft up and falling at a rate of 1/2 ft/sec?