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Add the first 2 numbers then divide the sum obtained by the third number to get the final result, ie.

$\frac{7+8}{5} = \frac{15}{5} = 3$

$\frac{9+5}{7} = \frac{14}{7} = 2$

$\frac{7+5}{3} = \frac{12}{3} =\boxed{4}$ .