The question asks to find the value of the 5th term of the sum:

I just did it by hand by inputting k=1, then k=2 and so on till k=5 and I summed them all up. I got 19.41. However, the answer key says 4. Can anyone tell me how to do this question. Also, is there some general formula for these types of questions, instead of doing it the way I did.