Mashaal Masha
$$8x+7y=9$$ $$24x+21y=27$$

For each real number $r$, which of the following points lies on the graph of each equation in the $xy$-plane for the given system?
Difficulty: Hard
A: 

$(r,-\frac{8r}{7}+\frac{9}{7})$

B: 

$(-\frac{8r}{7}+\frac{9}{7},r)$

C: 

\((-\frac{8r}{7}+9,\frac{8r}{7}+27)\)

D: 

$(\frac{r}{3}+9,-\frac{r}{3}+27)$

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