Find the amount of water displaced by a solid spherical ball of diameter $0.21 \, m$. (in $, m^3$)

Twenty-seven solid iron spheres,each of radius $r$ and surface area $S$,are melted to form a single sphere with surface area $S^{\prime}$. Find the radius $r^{\prime}$ of the new sphere. (in $r$)

$A$ right circular cylinder just encloses a sphere of radius $r$ (see figure). Find:
$(i)$ Surface area of the sphere,
$(ii)$ Curved surface area of the cylinder,
$(iii)$ Ratio of the areas obtained in $(i)$ and $(ii)$.

The height of a cone is $15 \, cm$. If its volume is $1570 \, cm^3$,find the radius of the base. (Use $\pi = 3.14$) (in $, cm$)

$A$ child is playing with building blocks, which are in the shape of cubes, and has built a structure as shown in the figure. If the edge of each cube is $3 \, cm$, find the volume of the structure built by the child. (in $cm^3$)

Find the total surface area of a hemisphere of radius $10 \, cm.$ (Use $\pi = 3.14$) (in $cm^2$)