If $f:R \to R$ satisfies $f$(x + y) = $f$(x) + $f$(y), for all x, y $ \in $ R and $f$(1) = 7, then $\sum\limits_{r = 1}^n {f\left( r \right)} $ is

Question

${{7n\left( {n + 1} \right)} \over 2}$

${{7n} \over 2}$

${{7\left( {n + 1} \right)} \over 2}$

$7n + \left( {n + 1} \right)$

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