Chemistry atom economy/ percentage yield question help!

1. Titanium can be extracted from its ore by two different methods. One uses a more reactive metal to displace the titanium:
TiO2 + 2 Mg → Ti + 2 MgO
The second method is electrolysis of the ore. The overall reaction for this method is:
TiO2 → Ti + O2
a. Calculate the atom economy for each reaction.
b. Which method is more sustainable? Explain.

For the first reaction I got an atom economy of 37.3% and second reaction 60.0%.
Is this correct?
Also, what reasoning do I use for part b? ( would I mention how the second reaction is more sustainable as it has a higher atom economy?)