The correct answer is "It's a primary source because it's firsthand information".
When we're presented with a statistical study of a certain topic, we're dealing with hard facts. A statement addressing "Percentage of College Degrees Awarded to Women" isn't making any assumptions on the matter and the tone of the phrase is neutral as opposed to personal (like you would find in a diary for example). Also, it's not an opinion that someone is giving through speech, but rather the expression of a mathematical calculation that someone made through the observation of certain data firsthand. That's why it is a primary source.
Hope this is helpful!