Hi, thank you for posting your question here at Brainly.
If you illustrate the problem, it forms a right triangle. The vertical feet is equal to 1200 feet. Then the slope of the mountain represents the hypotenuse of the triangle. To know the angle between the slope and the vertical height, we use cosine function:
cos theta = 1200/2400
theta = 60 degrees
But the angle of elevation refers to the angle the slope of the mountain makes with the horizontal. Thus, the angle is
180 -90 - 60 = 30 degrees
