Question 1100401
The difference between terms is {{{-6}}}. 
{{{d=-6}}}
.
.
{{{a[1]=204}}}
.
.
The sum of a arithmetic progression is,
{{{S[n]=(n/2)(2a[1]+(n-1)d)}}}
So,
{{{S[50]=(50/2)(2(204)+(50-1)(-6))}}}
{{{S[50]=25(408-49(6))}}}
{{{S[50]=25(114)}}}
{{{S[50]=2850}}}