Let us say A and B split their share of the task and started doing their respective shares simultaneously.
Let’s say A takes A days to finish the task. Therefore, B takes A + 12 days to finish the entire task.
A has to finish 40% of the task, since B is doing the rest. So A will only take 2A/5 number of days.
B only has to finish 60% of the task, so B will take (3(A+12)/5) number of days.
But as we know, B starts working along with A and finishes 12 days after A stops working.
So, (3(A+12)/5) = ((2A)/5+12)
3A + 36 = 2A + 60
A = 24; B = 36 days.

Let the capacity of the tank be C.
Rate of Pipe A = C/A  
Rate of Pipe B = C/B  
Rate of Pipe A and Pipe B together = C/A + C/B = C/8  

 C/12 + C/B   = C/8  
C/B   = C/8 – C/12 = C/24  
Pipe B independently will take 24 hours to fill the tank.

Initially, net flow in the tank = 40 litres/ 8 minutes = 5 litres/minute
Now, the increase in outflow should be greater than 5 litres/min for the tank to fill up.
Increase in outflow = 1.5x – x = 0.5x
Only in option C, 0.5 * 12 = 6 litres/min > 5 litres/min

Suraj took 23 minutes to finish the remaining work = 23/40  
Work finished by Ajay and Suraj together = 17/40  
Time taken = {17/40}/{(1/45)+(1/40)} =  17/ {8/9+1}  

17/ {17/9} = 9 mins

Length of wire all 3 of them can lay in a day = 432/8 = 54 m
On an average, 54/3 = 18 m will be laid by each which as per question should be the length Bibhuti can lay in a day.
Therefore, Anuj = 18 – x ; Chandu = 18 + x
Given,
7 * (18 – x) = 5 * (18 + x)
126 – 7x = 90 + 5x
=> 36 = 12x
=> x = 3
Therefore, Anuj in a day = 18 – 3 = 15 m