Empirical formula of Glauber's salt
Your approach seems correct, however you seemed to have made a few computation errors. First of Sodium's molar mass is $ 23 \ce{g/mol}$ and not 11. 

So assuming a total mass of 100g, we can re-interpret the given percentages as follows: 

mass of sodium = 14.3 g

mass of sulphur = 10 g

mass of oxygen = 19.9 g 

(note: the percentage you provided seems incorrect, the percentages add up to 91, not a 100. I've changed this data point to get the correct result.)

mass of water = 55.8 g

Dividing these by their respective molar masses to get no. of moles:

no. of moles of sodium  = 0.62

no. of moles of sulphur = 0.31

no. of moles of oxygen  = 1.2 

no. of moles of water   = 3.1

The ratio we get is 2:1:4:10. Thus, the empirical formula is $\ce{Na_2SO_4.10H_2O}$