$$

Hemodialysis is a procedure that a patient who has limited or virtually nonexistent kidney function undergoes to remove both waste products and extra fluid from his or her bloodstream. Blood from an artery of a hemodialysis patient is diverted into an artificial kidney where the blood enters numerous tiny fibers. An aqueous salt solution called dialysis fluid flows around these fibers. Waste products, most notably urea, and excess fluid within the blood pass through the fibers and into the dialysis fluid. The purified blood returns to the bloodstream through a vein.

Consider the schematic of an artificial kidney. After a certain amount of time in dialysis treatment, blood entering the dialysis machine from an artery has a flow rate of $323\mathrm{.}0m\frac{L}{m}in$ and a concentration of $1\mathrm{.}540mg$ urea $\frac{?}{mL}.$ The flow rate of the dialysis fluid entering the machine is $770\mathrm{.}0m\frac{L}{m}in.$ Blood leaving the dialysis machine has a flow rate of $317\mathrm{.}0m\frac{L}{m}in$ and a concentration of $1\mathrm{.}444mg$ urea $\frac{?}{mL}.$

What is the rate of urea removal from the blood stream?

rate of urea removal: $ng$ urea$/$min

If the flow rate of dialysis fluid leaving the artificial kidney is approximately the same as the flow rate of dialysis fluid into the artificial kidney, what is the concentration of urea in the waste dialysis fluid?

urea concentration: $mg$ urea$/$mL

People with kidney failure may also experience fluid buildup if their kidneys are no longer capable of producing enough urine. Thus, because it lessens water retention, the fluid removal aspect of kidney dialysis is also important. However, if fluid is removed too quickly, the patient may experience dangerous drops in blood pressure. For an average$-$sized patient, a removal of $350m\frac{L}{?}$ hour is considered safe. In the dialysis example given, how much fluid is removed from the blood in milliliters per hour?