Question 1034993
The formula for this is
{{{S[n] = (n/2)(a[1]+a[n]) = (n/2)(2a[1] + (n-1)d)}}}
{{{S[70] = (70/2)(2*(-6) + (70-1)*3)}}}
{{{S[70] = 35(-12 + 69*3) = 35(195) = 6825}}}