9514 1404 393
Answer:
4 feet
Explanation:
Desmos is useful for finding the answer to this. The problem statement tells you the angle with the x-axis is 75°. If we put the ladder in the first quadrant, the slope will be -tan(75°). We can raise its end to the 15 ft level by making the y-intercept be 15. Then the x-intercept answers the question: 4 ft.
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Additional comment
The angle mode needs to be set to Degrees in the Desmos settings for this equation to produce the correct graph.