The pharmacy receives the following PN order. How many milliliters of potassium phosphate (each mL contains 3 mmol of phosphate and 4.4 mEq of potassium) should be added to the PN to fulfill the phosphate requirements?

(Answer must be numeric; no units or commas.)

Item/Quantities:
- Dextrose: 270 g
- Amino acids: 60 g
- Sodium chloride: 38 mEq
- Sodium acetate: 16 mEq
- Potassium: 40 mEq
- Magnesium sulfate: 10 mEq
- Phosphate: 21 mmol
- Calcium: 4.45 mEq
- MVI-12: 5 mL
- Trace elements: 1 mL
- Vitamin K-1: 0.5 mg
- Famotidine: 10 mg
- Regular insulin: 40 units
- Sterile water: qs ad 980 mL

To calculate how many milliliters of potassium phosphate are needed to fulfill the prescription of 21 mmol of phosphate, we utilize the concentration provided for the potassium phosphate solution. Since each milliliter of the solution contains 3 mmol of phosphate, we can set up a simple division to find the required volume.

The prescription requires 21 mmol of phosphate. The solution contains 3 mmol of phosphate per milliliter. Hence, the calculation is as follows:

Volume required = Total phosphate required / Concentration of phosphate per mL
Volume required = 21 mmol / 3 mmol/mL
Volume required = 7 mL

Therefore, 7 mL of the potassium phosphate solution should be added to the PN to meet the phosphate requirements.