To find how many milliliters of the drug will be made, you will use proportions to solve for how much of compound a you will need with the indicated amount for compound b.
compound a 5 mL x 77 385 ml
compound b 4 ml x 77 308 ml
Add the two amounts together to get a total: 385 + 308 = 693 mL
There will be 693 mL of the drug.
