Can you please help me with the steps to figure out this question?

Can you please help me with the steps to figure out this question?

There are about 250 million molecules of hemoglobin in each red blood cell. Considering that all of the heme molecules are binding oxygen and that the red blood cell volume is about 0.1 pL, what is the concentration of O2 in a red blood cell? (for comparison, water at 37 degrees C contains about 0.4 mM dissolved O2) Please show work.