Answer:
Using tangent ratio:

As per the statement:
A surveyor measures the angle of elevation to a point on a mountain to be 18 degree.
Angle of elevation
= 18 degree.
It is also given that:
the point on the mountain is horizontally 4 miles away from the surveyor.
Let y be the vertical change in elevation from the point where the surveyor is standing to the point on the mountain.
See the diagram as shown below in the attachment
we have;
Opposite side = y miles and adjacent side = 4 miles
Using tangent ratio:

then;

Multiply both sides by 4 we have;

or
miles.
Therefore, 1.3 miles is the the vertical change in elevation from the point where the surveyor is standing to the point on the mountain