Question 918715
d = 3
{{{a[n] = a[1] + (n-1)d}}}
{{{a[n] = 2 + (n-1)3}}}
{{{a[n] =3n-1}}}

{{{a[n] =3n-1 = 59}}}, n = 20
{{{S[n]=(n(a[1]+a[n]))/2}}}
{{{S[20]=20(61)/2}}} = 610