Notice the smaller range and values of the experiment with cow manure (smaller box diagram and also located at smaller values of total energy.
The banana mixture clearly generates a wider box diagram (so less consistent) and also located at higher values (to the right).
Therefore, the answer we choose is the last one (bottom right) that says that the cow manure data is more consistent than the other one, and also, since the mashed banana data is so much higher, combined with the previous will clearly give larger amounts of biogas.
Please select the bottom right option.