Find the perimeter of a rectangle in which one side is 3 cm long and the other side is 2 times longer.

Find the length of the second side of this rectangle.

According to the condition of the problem, the length of one side of this rectangle is 3 cm, and the other side of this rectangle is 2 times longer than its first side, therefore, the length of the second side of this rectangle is:

3 * 2 = 6 cm.

Find the perimeter p of a given rectangle as the doubled sum of the length and width of this rectangle:

p = 2 * (6 + 3) = 2 * 9 = 18 cm.

Answer: the perimeter of this rectangle is 18 cm.

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