please help with these three pharmacology questions

Note: These last three questions deal with Therapeutic Drug Monitoring: A cat is receiving sustained-release theophylline once daily at 12mg/kg. A serum sample taken at 3 hours represents the peak at 13.1mcg/ml. The trough sample taken before the next dose contains 3.8mcg/ml. The therapeutic range for theophyliine is considered to be 10 to 20mcg/mL. Assuming first-order absorption and elimination and no change in the dosing interval, what dose would produce a trough concentration of 10mcg/ml ? (Answer to one decimal point.) Question 18 1 pts A cat, weighing 7 pounds, has a PCV of 8%. How many mls of blood will you need to give to raise its PCV to 28 , provided that the donor has a PCV of 48 . Assume that the Vd for blood in the cat is 66ml/kg. (Answer in a whole number.) Question 19 1pts A dog weighing 62 pounds, has a serum sodium of 122mEq/L. How many mls of 0.9% saline that contains 154mEaL. of sodem will you need to give to raise the serum sodium to 155mEq/L ? Assume that the Vd for sodium is 0.2L/Kg : (Answer in a whole number)