Question 826541
{{{a[n]=76}}}
{{{d=2}}}
{{{a[1]=-2}}}

solving the arithmetic equation {{{a[n]=a[1]+(n-1)d}}} for n yields 

{{{
n=(a[n]-a[1])/d+1 = (76--2)/2+1=40
}}}


{{{
S[n]=(n/2)(a[1]+a[n])=
S[40]=(40/2)(-2+76)=1480
}}}