The empirical formula is BH₃. Its B:H ratio is 1:3.
Assume that you have 100 g of the compound.
Then you have 78.14 g B and 21.86 g H.
Now, we must convert these masses to moles and find their ratios.
From here on, I like to summarize the calculations in a table.
Element Mass/g Moles Ratio Integers
B 78.14 7.2285 1 1
H 21.86 21.686 3.0001 3
The empirical formula is BH₃.