A triangle has side lengths measuring 3 x cm, 7 x cm, and h cm. Which expression describes the possible values of h , in cm?

For three lengths to form a triangle, the third side must be greater than the difference of the other two sides and less than their sum. Here, that gives 7x − 3x < h < 7x + 3x, so 4x < h < 10x. Therefore, the possible values are described by choice D.

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