Chromium Is an Ultratrace Metal in the Human Body with a Typical

Chromium is an ultratrace metal in the human body with a typical concentration of 5.0 mg in 75 kg of body mass. What is this concentration in units of parts per billion (ppb) ?

A) 6.7 $\times$ 10⁷ ppb
B) 6.7 $\times$ 10⁴ ppb
C) 67 ppb
D) 0.067 ppb
E) 0.67 ppb