On a square cardboard sheet of area 784 cm2,

$\because \quad$ Area of square $=784$

$\therefore \quad(\text { Side })^{2}=(28)^{2}$

$\Rightarrow \quad$ Side $=28 \mathrm{~cm}$

Since, all four are congruent circular plates.

$\therefore$ Diameter of each circular plate $=14 \mathrm{~cm}$

$\therefore$ Radius of each circular plate $=7 \mathrm{~cm}$

Now, area of one circular plate $=\pi r^{2}=\frac{22}{7}(7)^{2}$

$=154 \mathrm{~cm}^{2}$

$\therefore \quad$ Area of four circular plates $=4 \times 154=616 \mathrm{~cm}^{2}$

$\therefore$ Area of the square sheet not covered by the circular plates $=784-616=168 \mathrm{~cm}^{2}$