233

a)
9\equiv16\equiv23\equiv2\ \left(mod\ 7\right)
b)
2\cdot2\equiv2\cdot5\equiv2\cdot8\equiv1\ \left(mod\ 3\right)
c)
5\cdot1\equiv5\cdot3\equiv5\cdot5\equiv3\ \left(mod\ 2\right)