Find the n th partial sum of the arithmetic sequence. $9,16,23,30,37,\dots ,n=10$

A) 440
B) 790
C) 405
D) 395
E) 880

We can use the formula for the nth term of an arithmetic sequence:

$$a_n=a_1+(n-1)d$$

where $a_1$ is the first term, $d$ is the common difference, and $n$ is the term we want to find.

For this sequence, we have:

$$a_n=9+(n-1)7$$

We want to find the 10th partial sum, which is the sum of the first 10 terms:

$$\begin{array}{rl}{S}_{10}& =9+16+23+\dots +a_{10}\\ & =9+(9+7)+(9+2\cdot 7)+\dots +(9+9\cdot 7)\\ & =10\cdot 9+7\cdot (1+2+\dots +9)\\ & =90+7\cdot 45\\ & =\boxed{405}\end{array}$$

Therefore, the best choice is (C).