Answer:
The correct option is B) 12.
Step-by-step explanation:
Consider the provided information.
Working alone at its constant rate, pump X pumped out ¼ of the water in a tank in 2 hours.
As we know:  ,
, 
The rate of pump X is 
 of the water is pumped out of the tank, that means only
 of the water is pumped out of the tank, that means only  is left to be pumped out.
 is left to be pumped out.  
All 3 pumps pumped out the remaining  of the water out in 3 hours.
 of the water out in 3 hours.
The combined rate of all three pumps is:  
Pump Y, working alone at its constant rate, would have taken 18 hours to pump out the rest of the water. 
The rate of pump Y =  
Let z is the time taken by pump Z, then the rate of pump Z is  .
.
Therefore,

Multiplying both sides by 24 z.

Hence, the correct option is B) 12.