Barium Is a Nonessential Element in the Human Body, but Some

Barium is a nonessential element in the human body, but some organisms build exoskeletons using barium sulfate, which has a K_sp of 1.1 *10^-10 at 25°C. How many grams of barium are there in 1.0 L of a saturated solution of barium sulfate at 25°C?

A) 4.1 $\mu$ g
B) 1.4 mg
C) 3.7 mg
D) 7.3 $\mu$ g
E) 15 ng