Easy math question (geometric series, find next 3 terms)

they give you 5+k, 5, and 5-k and then you have to find the next three in the series...im so confused, help please!

What has happened between each term

5 + k, and 5 ( a subtraction of k)

5 and 5 - k ( a subtraction of k)

the 4th term, will be the 3rd term minus k
(5 - k) - k = 5 - 2k

the 5th term will be the 4th term minus k
(5 - 2k) - k = 5 - 3k

And the 6th term will be 5 - 4k

The ratio between any 2 successive terms in a geometric series will be the same. That is:

5 / (5 + k) = (5 - k) / 5

Solve for k

5 * 5 = (5 - k) * (5 + k)
25 = 25 - k^2
0 = k^2
k = 0

5 + 0 , 5 , 5 - 0 =>
5 , 5 , 5

What do you think the next 3 terms will be?

This is an arithmetic series: each term is k less than its predecessor.