Shown in the figure is a 7-hour clock and the table for clock addition in the
7-hour clock system.
$$
\begin{array}{|c|c|c|c|c|c|c|c|}
\hline \oplus & \mathbf{0} & \mathbf{1} & \mathbf{2} & \mathbf{3} & \mathbf{4}
& \mathbf{5} & \mathbf{6} \\
\hline \mathbf{0} & 0 & 1 & 2 & 3 & 4 & 5 & 6 \\
\hline \mathbf{1} & 1 & 2 & 3 & 4 & 5 & 6 & 0 \\
\hline \mathbf{2} & 2 & 3 & 4 & 5 & 6 & 0 & 1 \\
\hline \mathbf{3} & 3 & 4 & 5 & 6 & 0 & 1 & 2 \\
\hline \mathbf{4} & 4 & 5 & 6 & 0 & 1 & 2 & 3 \\
\hline \mathbf{5} & 5 & 6 & 0 & 1 & 2 & 3 & 4 \\
\hline \mathbf{6} & 6 & 0 & 1 & 2 & 3 & 4 & 5 \\
\hline
\end{array}
$$
a. How can you tell that the set \(\\{0,1,2,3,4,5,6\\}\) is closed under the
operation of clock addition?
b. Verify one case of the associative property: \((3 \oplus 5) \oplus 6=3
\oplus(5 \oplus 6)\)
c. What is the identity element in the 7-hour clock system?
d. Find the inverse of each element in the 7-hour clock system.
e. Verify two cases of the commutative property: \(4 \oplus 5=5 \oplus 4\) and
\(6 \oplus 1=1 \oplus 6\)