I need little help for solving the following problem:
The value of $\alpha$ for which $G=\{\alpha,1,3,9,19,27\}$ is a cyclic group under multiplication modulo $56$ is which of the following?
(a)$5$,(b)$35$,(c)$25$,(d)$15$.
Can someone point me in the right direction? Thanks in advance for your time.