let's assume ur ans: 4500mL is correct
& we work forward according to qn to check ans, k?

total is 4500 mL
give Josh: 2/9 x 4500 = 1000 mL
left: 3500mL

give Michelle: 800mL
left: 3500-800 = 2700mL

give Michael: 3/10 x 2700mL = 810mL

but this contradict ur own calculation of Michael getting 600mL


so do u agree that 4500mL is incorrect ans?

No! Finally l understood! Thank you very much

I mean YES

Last step is incorrect.

900 x 4 = 3600ml. (Ans)

Thanks!