Hi
the answer for 3rd question is
Rate of infusion=CssxCL
Css=steady state concentration, Cl=clearance
Cl=Vd x Ke
=0.5l/kg, for 155lbs it is 35.23litres,Ke=0.693/t1/2
Ke=0.693/6=0.1155
Cl=35.23x0.1155=4.068litres/hour
we need to calculate dose for doing Css. Vd=Dose/Cp
Vd=35.23=dose/20mcg/ml 20mcg=0.02mg/ml
since Vd is in litres, 0.02x1000=20 mg in litres
Dose=35.23x20=704.6mg
Css=Dose/Vd= 704.6/35.23=20mg/litres
Rate of infusion-=CssxCl=20x4.068litres/hour=81.36mg/hour
as the answer inminutes, you divide by 60 to get 1.35mg/min