How do i work out the purity and the yield of Barium Thiosulfate?

I used 5 grams of Barium Nitrate and 5 grams of Sodium Thiosulfate to make Barium Thiosulfate. I got in the end 1.54grams of Barium Thiosulfate. The molecular m is 249, but i do not know how to work out the purity or yield of this, if anyone could post how to because i need to understand this for my course.