It's always a good idea to start with the equation!
Now we look at the stoichiometry of the equation - which just means the ratio of different components. These ratios are given by the coefficients - numbers in front of a component.
So here, we can see that for every 2 moles of Sodium Oxide we will get 4 moles of Sodium. So we have a ratio of 2:4 or 1:2.
In the question, there are 1.87 moles of Sodium Oxide so following our ratio there will be
I hope this helps: let me know if I can do anything else:)