An isolated storm of 3 hours occurred over a catchment area in the following manner
\begin{array}{|c|c|c|c|c|}
\hline Catchment \\
\hline 15 & $0.5$ & $0.4$ & $2.5$ & $1.6$ \\
\hline 35 & $1.0$ & $0.8$ & $3.0$ & $2.1$ \\
\hline 50 & $0.8$ & $0.6$ & $2.6$ & $1.9$ \\
\hline
\end{array}
Total rainfall excess (in cm, rounded off to one decimal place) over the catchment for the above storm is
