1) Subtract from the perimeter of the rectangle the sum of its three sides and find the value of the fourth side: 20 – 14 = 6 (cm);
2) Since the sides of the rectangle are pairwise equal, we calculate the doubled value found from the sides: 6 · 2 = 12 (cm);
3) Subtract from the perimeter the doubled value of its two equal sides and determine what the sums of the other two equal sides are equal to: 20 – 12 = 8 (cm);
4) Find out the size of the other side of the rectangle: 8: 2 = 4 (cm);
5) Using the formula, we calculate the area of the rectangle: S = a b = 4 6 = 24 (cm ^ 2).
Answer: S = 24 cm ^ 2.
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