You will have to divide 353 millimeters by 4:
353 รท 4 = 88.25
now we have to multiply 88.25 by 9 (5+4), the total millimeters of only one portion of this drug
88.25 x 9 = 794.25
So he will make 794.25 millimeters of drug (that is if he has the part a too)
(If you should round 88.25 to 88, the answer would be 88 x 9 = 792)