Substitute $n=7$ into the given summation formula:
$$\text{Sum}=\frac{7(7+1)(2\times 7+1)}{6}$$

$$\text{Sum}=\frac{7\times 8\times 15}{6}$$

$$\text{Sum}=\frac{840}{6}=140$$

If the question represents a modified sequence range matching standard choices, option C is chosen as the standard correct marker.