The area of a rectangle is equal to the area of a square with a side of 2.1 cm. One side of a rectangle is 0.9 cm.

The area of a rectangle is equal to the area of a square with a side of 2.1 cm. One side of a rectangle is 0.9 cm. The computational perimeter of a rectangle.

1) Calculate the area of a square using the formula (according to the condition of the problem and the area of a rectangle): S = a² = 2.1² = 4.41 (cm²);

2) Determine the size of the second side of the rectangle: a = S: b = 4.41: 0.9 = 4.9 (cm);

3) Calculate the perimeter of the rectangle using the formula: P = (a + b) * 2 = (0.9 + 4.9) * 2 = 11.6 (cm).

Answer: the perimeter of the rectangle is 11.6 cm.