Erythrocytes phosphorylate glucose to glucose 6-phosphate with the help of the enzyme hexokinase instead of glucokinase. Hexokinase has a Km = 0.055 mM. How low would the blood glucose concentration have to fall to decrease the rate of glucose phosphorylation in the erythrocyte to 75% of Vmax? (Assume that the Michaelis-Menten equation is applicable.)