Find each limit$,$ if it exists. $($If an answer does not exist, enter DNE.$)$

$($a$)\underset{x}{lim}\frac{x^{7}3}{x^6-8}=$

$($b$)\underset{x}{lim}\frac{x^{7}3}{x^7-8}=$

$($c$)\underset{x}{lim}\frac{x^{7}3}{x^6-8}=$

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