Answer
$4.9~L/min$
Work Step by Step
We can find the volume rate of blood flow in $cm^3/s$:
$\pi~r^2~v = \pi ~(1.2~cm)^2~(18~cm/s) = 81.43~cm^3/s$
We can convert this volume rate of blood flow to units of L/min:
$81.43~cm^3/s\times \frac{1~L}{1000~cm^3}\times \frac{60~s}{1~min} = 4.9~L/min$
