Answer
$6.\overline6\ hr$
Work Step by Step
Find the total number of drops.
$1600\ mL\times\frac{10\ drops}{1\ mL}=16000\ drops$
Divide the number of drops by the flow rate to find the time.
$16000\ drops\div\frac{40/ drops}{1\ min}=16000\ drops\times\frac{1\ min}{40\ drops}=400\ min$
Convert to hours.
$400\ min=400\ min\times\frac{1\ hr}{60\ min}=6.\overline6\ hr$
