Need help on the following. Thanks.

0#1=2
Is # commutative, associative?


Construct an operation table for * on {1,2,3,4} where, a * b = "the remainder when axb is divided by 5"

Eg. 2 * 4 = 8/5 = 1R3 = 3
Is this operation closed? associative? commutative? what is the identity?

Solve the equations:
a) z * 3 = 1
b) b* (b * 2) = 3