Calculate the simple and weighted average from the following and account for the difference between the two:
$$
\begin{array}{|l|r|r|r|}
\hline \text { Price per ton }(R s) \text { . }) & 45.60 & 50.70 & 42.45 \\
\hline \text { Tons Purchased } & 135 & 40 & 25 \\
\hline
\end{array}
$$