(11.38 g/day)*(2.82ug/kg)*(17.5kg-day/mg)/20kg

Just looking at the numbers:
11.38 * 2.82*17.5/20

=561.603/20
=28.08015
But what should I have as the extension
g/kg or what?

g/day µg/kg kg day/mg 1/kg =

µg*g/mg *(1/kg) = 10^(-6)