The dose of fentanyl in mcg/kg/hr can be calculated by multiplying the concentration of fentanyl in the syringe (10 mcg/mL) by the rate at which it is being administered (0.45 mL/hr) and then dividing by the weight of the baby (1.5 kg).
This gives us a dose of (10 mcg/mL * 0.45 mL/hr) / 1.5 kg = 3 mcg/kg/hr. So the correct answer is a. 3 mcg/kg/hr.