Hello, thank you for taking the time to post your question!
His total pay would be
Total Pay = Base Salary + Commission
For this scenario that would be
Total Pay = 3000 + 3%(75000)
=3000 + 2250
=5250
So his pay for the month of January is $5,250
I hope that helps get you moving in the right direction! Feel free to reach out if you have any additional questions beyond that :)