If the two diagonals of a parallelogram are $72 \, cm$ and $30 \, cm$ respectively,then find its perimeter in $cm$.

In trapezium $ABCD$,$AB || CD$ and $AB = 2 \, CD$. Its diagonals intersect at $O$. If the area of $\Delta AOB = 84 \, cm^2$,then the area of $\Delta COD$ is equal to (in $cm^2$)

The hypotenuse and the semi-perimeter of a right triangle are $20\, cm$ and $24\, cm$,respectively. The other two sides of the triangle are

$A$ rectangular park $60 \, m$ long and $40 \, m$ wide has two concrete crossroads running in the middle of the park, and the rest of the park has been used as a lawn. If the area of the lawn is $2109 \, m^2$, then what is the width of the road? (in $m$)

On decreasing each side of an equilateral triangle by $2\, cm$,there is a decrease of $4\sqrt{3}\, cm^2$ in its area. The length of each side of the triangle is.........$cm$.

$A$ piece of wire $132 \, cm$ long is bent successively in the shapes of an equilateral triangle,a square,a regular hexagon,and a circle. Then,which has the largest surface area?