In the given diagram,the shaded portion represents a flower bed in a plot. If $m \angle O = 90^\circ$,$OB = 21 \, \text{m}$,and $OD = 14 \, \text{m}$,find the area of the flower bed in $\text{m}^2$.

As shown in the adjoining diagram,the length of the side of the square plot $ABCD$ is $50 \, m$. At each vertex of the plot,a flower bed in the shape of a sector with radius $10 \, m$ is prepared. Find the area of the plot excluding the flower beds. $(\pi = 3.14)$ (in $m^2$)

The ratio of the radii of two circles is $4: 5$. Then,the ratio of their areas is...........

If the radius of a circle is doubled,its area becomes $\ldots \ldots \ldots$ times the area of the original circle.

The radius of a circular ground is $90\, m$. Inside it,a road of width $10\, m$ runs around its boundary. Find the area of the road. $(\pi=3.14)$ (in $m^2$)

The diameter of a circle with area $38.5 \, m^2$ is $\ldots \ldots \ldots \ldots m$.