Triangle $ABC$ has vertices $A(0,8)$, $B(2,0)$, $C(8,0)$.  A vertical line intersects $AC$ at $R$ and $\overline{BC}$ at $S$, forming triangle $RSC$.  If the area of $\triangle RSC$ is 12.5, determine the positive difference of the $x$ and $y$ coordinates of point $R$.

Let's think step by step and output the final answer within \boxed{}.
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