This is an arithmetic progression where each term increases by 5: 5, 10, 15, 20, 25, so the next term is 30. The pattern is consistently adding 5 to each number (5+5=10, 10+5=15, etc.). Option A (40) would be skipping by 10s after 20, B (35) breaks the pattern, and D (25) repeats the previous term.