The aspirin substitute acetaminophen (C₈H₉O₂N) is produced by the following three-step synthesis:

I. C₆H₅O₃N(s) + 3H₂(g) + HCl(aq) → C₆H₈ONCl(s) + 2H₂O(l)

II. C₆H₈ONCl(s) + NaOH(aq) → C₆H₇ON(s) + H₂O(l) + NaCl(aq)

III. C₆H₇ON(s) + C₄H₆O₃(l) →C₈H₉O₂N(s) + HC₂H₃O₂(l)

The first two reactions have percent yields of 87% and 98% by mass, respectively. The overall reaction yields 3 moles of acetaminophen product for every 4 miles of C₆H₅O₃N reacted.

a. What is the percent yield by mass for the overall process?

b. What is the percent yield by mass of step III?