Question 1040989
From the sum,
{{{S[n]=(n/2)(a[1]+a[n])}}}
{{{196=(n/2)(-12+40)}}}
{{{392=n(28)}}}
{{{n=14}}}
.
.
{{{a[n]=a[1]+(n-1)d}}}
{{{40=-12+(14-1)d}}}
{{{13d=52}}}
{{{d=4}}}