Find the circumferences of the circle with a diameter 2.1 cm

The diameter of the circle is 2.1 cm.
Circumference of a circle = 2πr
Or circumference = πd
Circumference = π × 2.1 cm

$$\begin{gathered} =\frac{22}{7}\times 2.1 cm \\ =22\times 0.3 cm \\ =6.6 cm \end{gathered}$$