Given the word problem, we can deduce the following information:
1. Last week, your patient's doctor indicated that you should mix 60 milligrams of Medication A with 78 milligrams of Medication B.
2. This week, the doctor said to only use 65 milligrams of Medication B.
To determine the amount in milligrams of Medication A for this week, we first let x be the amount in milligrams of Medication A, and apply the process as shown below:
Therefore, 50 milligrams of Medication A should be mixed this week.