Hi, please help. urgent...

thank you so much in advance.

question: what is the order of 3^20(mod 31). Do I use the thm : suppose [a] has order e in z/mz then [a]^d has order e l (d,e) ?

I tried, but it doesn't seem to work corrrectly for me...:(

And also this problem,

find all units in Z/200Z. Do i have to test each number such as 1,3, 7, 9,..to 199? or is there a formula I can use.