Let us assume the total work which needs to be done is 120 units (LCM of 4,5 and 6 which are basically the numbers used in the question).

Therefore, the work completed by Ali and Moe in 1 hour = 120 units/4 hours i.e. 30 units/hour.

Now, we know that Ali is 5 times faster than Moe. So, if the total work was 30 units/hour, Ali would finish 25 units and Moe, 5 units.

So, if Ali were to finish the task alone, he'll need to finish 120 units at a rate of 25 units/hour. i.e. 120 units/ 25 units = 4.8 which translates to 4 hours and 48 minutes.

Hence, option C is the correct answer.

Hope it helps