Area of a rectangle $=$ ............

The sides of a triangle are $a \, cm$,$b \, cm$,and $c \, cm$. Also,its semi-perimeter is $s \, cm$. If $s - a = 10 \, cm$,$s - b = 15 \, cm$,and $s - c = 12 \, cm$,then $s = \dots \, cm$.

The diagonals of a rhombus are $40 \, cm$ and $42 \, cm$. Find its area in $cm^2$.

The shape of a field is a triangle. The measurements of the sides of the field are $51 \,m$,$52 \,m$ and $53 \,m$. Find its area. (in $,m^2$)

Write True or False and justify your answer.
The area of a triangle with base $4 \, \text{cm}$ and height $6 \, \text{cm}$ is $24 \, \text{cm}^2$.

If the sides of a triangular field are $290 \, m$,$290 \, m$,and $400 \, m$,find the area of the field in $m^2$.