Answer:
15, 75, and 30 in that order.
Explanation:
plug the number of weeks for x in the equation
you learn 15 new vocab words per week because you plug in 1 for x in the equation
you learn 75 words after 5 weeks because you plug in 5
you learn 90 words in 6 weeks and 60 words in 4 weeks, and 90-60=30, so you learn 30 more words after 6 weeks than after 4 weeks
hope this helped! good luck