13) Find the order of each of the following elements in the multiplicative group of units U(sub)p.

a. [2] for p=13

b. [5] for p=13

c. [3] for p=17

d. [8] for p=17

If you can tell me what units mean, and how to solve at least one of the problems, I think I should be able to do the rest. At this point, I don't know where to begin.

Thanks!