The area of shaded region of the adjacent figure is

Area of the shaded region Area of rectangle Area of 6 circles

$$\begin{gathered} =\left(30\times 20\right) - \left(6\times \frac{22}{7}\times 5\times 5\right) \\ =600 - 471.4 \\ =128.6 c{m}^2 \end{gathered}$$