Concentration of mercury in body
There are 1,000,000 mg in a kg (this is, mg/kg = ppm), so all you need to do is divide the mass of $\ce{Hg}$ by the mass of the person as-is (the units work out to ppm):

$$\left({30\,{\rm mg}\over 63.5\,{\rm kg}}\right)\cdot\left({{\rm ppm}\over {\rm mg\cdot kg^{-1}}}\right) = 0.47\,{\rm ppm}\,\ce{Hg}$$