Parabola

Let \(R\) be the focus of the parabola \(y^{2}=20 x\) and the line \(y=m x+c\) intersect the parabola at two points \(P\) and \(Q\).


Let the point \(G(10,10)\) be the centroid of the triangle \(P Q R\). If \(c-m=6\), then \((P Q)^{2}\) is :