Draw a rt. triangle: 
The bottom is the ground, the hypotenuse is the flight path, the upright is the line from the ground to the planes position after one minute (60 seconds). 
p = altitude of plane, h = flight path 
h = (275)(60) = 16500 
Using the law of sine: 
sin (18) = p/16500 
p = [sin(18)](16500) 
p= 5098.8 ft