The width of the rectangle is 21 cm and is 70% of the length. Find the perimeter of the rectangle.

Knowing what the width of this rectangle is and the ratio between its length and width, we will find the length of this rectangle.

According to the condition, the width of this rectangle is 21 cm and is 70% of the length.

Denoting the length of this rectangle by x, we get the following equation:

(70/100) * x = 21.

Solving the equation, we get:

(7/10) * x = 21;

x = 21 / (7/10);

x = 21 * (10/7);

x = 10 * 21/7;

x = 10 * 3;

x = 30 cm.

Knowing what the lengths are equal to the width of a given rectangle, we find its perimeter:

2 * (30 + 21) = 2 * 51 = 102 cm.

Answer: the perimeter of the rectangle is 102 cm.