the sum of an arythmetic sequence for first term, a1 and last term, an and up to the term, n is
\(s_n= \frac{n(a1+an)}{2}\)
n=58
a1=6
a58=405
\(s_{58}= \frac{58(6+405)}{2}\)
\(s_{58}= \frac{58(411)}{2}\)
\(s_{58}= \frac{23838}{2}\)
\(s_{58}= 11919\)
sum is 11,919
