I'm not sure because some months have a different amount of days so it will be hard to determine precisely. Without further due, lets begin...
Part B:
Lets say that each month has 4 weeks in it. That means go ahead and multiply 4 x 6 = 24, 24 is the amount of weeks total.
Then, do 13 x 24 which equals 312.
That means he earned 312 dollars.