AMC 12 2003b Problem 5

Many television screens are rectangles that are measured by the length of their diagonals. The ratio of the horizontal length to the height in a standard television screen is 4 : 3. The horizontal length of a "27-inch" television screen is closest, in inches, to which of the following?

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$\text {(A) } 20 \text {(B) } 20.5 \text {(C) } 21 \text {(D) } 21.5 \text {(E) } 22$