Question 929332
First find the sequence.
{{{a[n]=-11+5n}}}
Then find n for the last term.
{{{39=-11+5n}}}
{{{50=5n}}}
{{{n=10}}}
Then use the sum formula,
{{{S[n]=(n/2)(a[1]+a[n])}}}
{{{S[10]=(10/2)(-6+39)}}}
{{{S[10]=5(33)}}}
{{{highlight(S[10]=165)}}}