see the attached picture to better understand the problem
we know that
in the right triangle ABC
sin A=BC/AB
where
A------> is the angle of elevation of the mountain
BC--> opposite side angle A---> is the elevation of the mountain---> 2,100 ft
AB----> is the hypotenuse of the triangle-----> 2.75 miles
step 1
convert miles to feet
1 mile is equal to------> 5,280 ft
so
2.75 miles=2.75*5280-----> 14,520 ft
step 2
sin A=2,100/14,520-----> sin A=0.1446
A=arc sin (0.1446)------> A=8.32°
therefore
the answer is
the angle of elevation of the mountain is 8.32 degrees
