Quantitative Aptitude

The annual grain yield $Y$ (in $\text{kg/ha}$) and seasonal irrigation water applied $W$ (in $\text{cm}$) for five experimental plots are given below: $\begin{array}{|c|c|c|} \hline \textbf{Plot} & \textbf{Water Applied } W\text{ (cm)} & \textbf{Grain Yield } Y\text{ (kg/ha)} \\ \hline \text{P1} & 30 & 3600 \\ \text{P2} & 40 & 4400 \\ \text{P3} & 50 & 5000 \\ \text{P4} & 60 & 5400 \\ \text{P5} & 70 & 5600 \\ \hline \end{array}$ Calculate the marginal water productivity in $\text{kg/ha per cm of water}$ between Plot P1 and Plot P3. ________ (answer in integer).