$7\mathrm{.}4.$ a$)$ Calculate the pressure drop per centimeter length of the aorta when the blood flow rate is $25$ liter$/$min$.$ The radius of the aorta is about $1$ cm and the coefficient of the viscosity of blood is $4$x$10-3$ Pa$-$s$.$ b$)$ Calculate the total drop in blood pressure along a $30-$cm length of artery of radius $0\mathrm{.}5$ cm$.$ Assume that the artery carries blood at a rate of $8$ liter$/$min$.$