Answer:
28 million college students.
Step-by-step explanation:
We can represent all college students as x. This means that all part-time college students are
. Because all part-time college students are also equal to 8.6 million, we have
. To find the number of total college students, or x, we have to multiply by 100/31 to get rid of the fraction on the other side:

The left side of the equation evaluates as
. Because we are asked to round to the nearest million, we have to round to 28 million, which is the closest.
8x + 4y = 20
4y = 20 - 8x
y = 5 - 2x
Your best bet would be D.