The length and breadth of a rectangular field are in the ratio of 3:2.  If its perimeter is 600 mts, then the area in sq.mts is

$\Rightarrow 2\left(l+b\right)=600$

$\Rightarrow 3x+2x=300$

$\Rightarrow 5x=300$

$\Rightarrow x=60mts$

Length $=3\times 60=180mts$

Breadth $=2\times 60=120mts$

Area $=l\times b=180\times 120=21,600mt{s}^2$