Please explain how to get the answer for IGCSE O/L June 13 Alt to Practical

question 2. Link is below? Below is the link for the 0625/62 May/June 13 alt tp pract. paper. I have the marking sceme with me but it does not explain how they got the answer. I need to find the answer for question number 2 part (d).

Paper -
http://share.pdfonline.com/936f3128bc4d46fc9253d298b636f6fa/0625_s13_qp_62.htm

Mark Scheme -
http://olevel.sourceforge.net/papers/0625/0625_s13_ms_62.pdf

Please please please explain how they got the answer to be 40-50 cubic centi meters.

Thank you so very much!!!
Question from Heat and Temperature