Suppose you put 50 ml of water in the can instead of 100 ml and heated it to 40 degrees instead of 20 degrees. in what ways if any would this affect the results of the investigation

Once these values are put into the equation delta Q=mc delta T it will give you the same value for Q (change in energy) if the same fuel is used 50mL will mean it gets heated quicker making the experiment quicker 200mL would take longer to heat for the same change in temperature causing a longer experiment.