\(\begin{array}{c|c}
\text{Units of quantity} & \text{Total utility} & \text{Marginal utility} \\
\hline
0 & – & – \\
\hline
1 & 10 & 10 \\
\hline
2 & 15 & 5 \\
\hline
3 & 17 & 2 \\
\hline
4 & 18 & 1 \\
\hline
5 & 18 & 0 \\
\end{array}\)
The table illustrate the law of