Hi, I have an issues with solving this problem.

Let the summation of a_{n}from n=1 to infinity be a series and let m be in the natural numbers. Show that the summation of a_{n}from n=1 to infinity converges IFF the summation of a_{m+n}from n=1 to infinity converges, and that (the summation of a_{n}from n=1 to infinity) = S_{m}+ (the summation of a_{m+n}from n=1 to infinity converges).

I understand that this problem is basically telling you to prove the properties of the Tails of series, but I'm not sure how I would go about proving it. And sorry for all the long typing for all the summation things, I don't know how to type it out the proper way.