# Gravitation-Where am I stuck?

Four particles of masses $$m$$, $$2m$$, $$3m$$ and $$4m$$ are placed in a clockwise manner at $$4$$ corners of a square of side $$a$$. Find the gravitational force acting on a particle of mass $$m$$ placed at the center.

If the answer is in the form $$\frac { m\sqrt { n } G{ M }^{ 2 } }{ { a }^{ 2 } }$$, find $$m+n$$ .

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