Determine whether the tables in Exercises 11 through 18 represent functions or not. Assume that the input is in the left column or top row. Explain your answer.
$$\begin{array}{|c|c|}\hline \text { Years in College } & \text { Credits Earned } \\\hline 1 & 30 \\2 & 75 \\1 & 36 \\3 & 60 \\4 & 120 \\5 & 100 \\1.5 & 50 \\\hline\end{array}$$