That's a right triangle with hypotenuse 3000 and the height y is the side opposite the elevation angle of 15 degrees.
[tex]y = 3000 \sin 15^\circ[/tex]
We can actually compute [tex]\sin 15^\circ[/tex] exactly but I won't bother.
[tex]y \approx 776 \textrm{ feet}[/tex]
