Question 1102021
Check the common difference to successive terms and see where the sequence is going.  {{{-5/3}}} is the common difference, and makes the sequence DECREASE.


General term:  {{{5+(n-1)(-5/3)}}},  or better,  {{{highlight_green(5-(5/3)(n-1))}}}.


What is the index for the term,  {{{-15}}} ?
{{{5-(5/3)(n-1)=-15}}}-----solve this for n.