"A student" doesn't register for 46,140 credits, unless he wants to be very very busy.
If ALL of the students on campus register for 46,140 credits, then many colleges
would estimate the number of full-time students by using the formula
f = n / 15 = 46,140 / 15 = 3,076 students.
That's not the formula for 'n'. 'n' is the total number of credits for the semester,
and the question tells you what 'n' is. Knowing 'n', the formula helps you find 'f'.