Answer: approximately 7525 feet
A more accurate value is 7,524.6679636332 feet, but even that isn't fully exact.
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Step-by-step explanation:
The change in height, or delta height value, is 11200-9000 = 2200 which is the vertical component of the right triangle shown below. This side is opposite the reference angle, aka the angle of elevation 17°
The hypotenuse is x, which is the length of the trail. Assume we're dealing with a flat and straight surface. Of course realistically the ground is very likely going to be bumpy with various curved complexities; but we'll simplify things greatly.
We'll use the sine ratio to find x.
sin(angle) = opposite/hypotenuse
sin(17) = 2200/x
x*sin(17) = 2200
x = 2200/sin(17)
x = 7,524.6679636332
Assuming your teacher wants you to round to the nearest whole number, then we'd get to 7525 feet