The formula 1+2+3+...+n = (n(n+1))/2 is true for all integers n>=1. Use this fact to solve each of the following problems:

If n is an integer and n>=1, find a formula for the expression

3+3(2)+3(3)+...+3(n)+n

Is this correct?

3+3((n(n+1))/2)+3

3+(3/2)(n(n+1))+3

3+(3/2)(n^2+n)+3