The diagonal (red line) is 20 feet long and forms a 35° angle with one side of the pool. What is the total cost to build one of the adjacent sides to the 35° angle if the cost to build the pool's sides is $⁢50 per foot?

The 20-foot diagonal is the hypotenuse of a right triangle, and the side adjacent to the 35° angle is found using cosine: cos(35°) = adjacent side ÷ 20. So the side is 20 × cos(35°) ≈ 16.383 feet. At $50 per foot, the cost is 16.383 × $50 ≈ $819.15, which is choice B.

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