How much lithium and how much oxygen you need to take to get 80g. lithium oxide?

Given:
m (Li2O) = 80 g

To find:
m (Li) -?
V (O2) -?

1) 4Li + O2 => 2Li2O;
2) n (Li2O) = m / M = 80/30 = 2.67 mol;
3) n (Li) = n (Li2O) * 2 = 2.67 * 2 = 5.34 mol;
4) m (Li) = n * M = 5.34 * 7 = 37.4 g;
5) n (O2) = n (Li2O) / 2 = 2.67 / 2 = 1.34 mol;
6) V (O2) = n * Vm = 1.34 * 22.4 = 30 liters.

Answer: The mass of Li is 37.4 g; O2 volume – 30 l.