Since all of the intervals are two years, we just need to find the smallest change:
For answer (1), it changed 12 (from 11 to 23)
Answer (2),  17 (from 16 to 33)
Answer (3), 19 (from 23 to 42)
Answer (4), 14 (from 33 to 47)

That’s it — 2 points!!