Four circular cardboard pieces,each of radius $7\, cm$,are placed in such a way that each piece touches two other pieces. The area of the space enclosed by the four pieces is.......$cm^2$.

$A$ cylindrical vessel of height $5\, cm$ and radius $4\, cm$ is completely filled with sand. When this sand is poured out,it forms a right circular cone of radius $6\, cm$. What will be the height of this cone? (in $cm$)

An open box is made of wood $2\, cm$ thick. Its internal length is $86\, cm,$ breadth $46\, cm$ and height is $38\, cm.$ The cost of painting the outer surface of the box at $Rs.$ $10$ per $m^2$ is? (in $Rs.$)

$A$ General,while arranging his men,who were $6000$ in number,in the form of a square,found that there were $71$ men leftover. How many were arranged in each row?

Three sides of a triangular field are $20\, m$,$21\, m$,and $29\, m$ long,respectively. The area of the field is.......$m^2$.

Four equal-sized circular plates of maximum diameter are cut off from a square paper sheet of area $784 \, cm^2$. The circumference of each plate is ...... $m$.