The magnetic field existing in a region is given by $\vec { B } = 0.2 ( 1 + 2 x ) \hat { k } \mathrm {~T}$. A square loop of edge 50 cm carrying 0.5 A current is placed in $x - y$ plane with its edges parallel to the $x - y$ axes, as shown in figure. The magnitude of the net magnetic force experienced by the loop is $\_\_\_\_$ mN.