The slanted roof has a horizontal base of 12 feet and a vertical height of 9 feet. what is the total cost to cover the slanted roof with shingles if it costs $⁢20 per foot?

The slanted length is the hypotenuse of a right triangle with legs 12 feet and 9 feet. Using the Pythagorean theorem, its length is √(12² + 9²) = √225 = 15 feet. At $20 per foot, the cost is 15 × $20 = $300, so the correct choice is 300 dollars.

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