Question 727805
Finding or evaluating finite arithmetic series is {{{(n/2)(2a[1]+(n-1)d)}}}, where n is the index of the final term, {{{a[1]}}} is the first term, and d is the common difference between terms.


Your example would use the expression for the sum as {{{(n/2)(2*3+(n-1)*3)}}}, and because you want this value to be "not less than 2000", you want the inequality statement,
{{{highlight((n/2)(2*3+(n-1)*3)>=2000)}}}.  Solve for n.