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