The radius of a circle is increasing uniformly at the rate of 0.3 centimetre per second. At what rate is the area increasing when the radius is 10 cm?

(Take π = 3.14.)

The side of a square is increasing at the rate of 0.2 cm/s. Find the rate of increase of the perimeter of the square.

The radius of a circle is increasing at the rate of 0.7 cm/s. What is the rate of increase of its circumference?

The side of a square sheet of metal is increasing at 3 centimetres per minute. At what rate is the area increasing when the side is 10 cm long?

The radius of a circular soap bubble is increasing at the rate of 0.2 cm/s. Find the rate of increase of its surface area when the radius is 7 cm.