Explanation:

- Pipe A fills the tank in 32 hours. So, A fills 1/32 of the tank in 1 hour.

- Pipe B fills the tank in 28 hours. So, B fills 1/28 of the tank in 1 hour.

- If both pipes are opened alternately for 1h each (A first, then B), in 2 hours, the tank filled = 1/32 + 1/28

- LCM of 32 and 28 is 224.

- 1/32 = 7/224 and 1/28 = 8/224. So, in 2 hours, 7/224 + 8/224 = 15/224 is filled.

- In x pairs of 2 hours (2x hours), (15x/224) is filled.

- To fill the full tank:

15x/224 ˜ 1 ? x ˜ 224/15 ˜ 14.93 pairs (~15 pairs).

- After 15 pairs (30 hours), 15 × 15 = 225/224 (more than full, so it will be filled just before 30 hours).

- So, option:4 - 24 is closest to actual answer (rounded to nearest integer: 29.8 ˜ 30 hours).

- Correct option is 2 – 30 hours.

- Other answers (22, 36, 24) are not matching the calculated time.