please answer this question

Let the capacity of the cistern be the LCM of 69 and 46 i.e. 138 units.

⇒ The efficiency of Pipe A = 138/69 = 2 units

⇒ The efficiency of Pipe B = 138/46 = 3 units

Since Pipe B is draining, the efficiency of pipe B will be -3.

Now, pipe B starts working first.

⇒ Work done by pipe B and pipe A in 2 hours = -3 + 2 = -1 unit

Now, -1 unit = 2 hours

⇒ -135 units = 135 × 2 = 270 hours

Now, pipe B will be working for the next hour for -3 units and the tank would be empty.

⇒ Total time = 270 + 1 = 271 hours = 11 days 7 hours

Regards!