Please show the steps . The answer is 23.76. This is a simple problem, I'm just missing a step or two.

2 B5H9 + 12 O2 => 5 B2O3 + 9 H2O

How many molecules of B2O3 will be made with 30.9 g of H2O? Take the log of your answer and enter it to 2 decimal places.