Since Carla cannot work on a Monday and 2 operator have to be on duty, Bob and Amy must work on Monday.
We can eliminate option E since it says that none of the operators work for four consecutive days in a week.
We know that Bob works for a maximum of three days and we know he has to work on Monday, Tuesday and Friday. This means that his days are complete and he will not work on Wednesday and Thursday.
Since 2 operator have to work on a day, Amy and Carla will work on Wednesday and Thursday.
We know Carla must work on Wednesday and Thursday. We can eliminate options B and C, leaving us with A and D.
We know that Amy cannot work for 4 consecutive days as that is the rule. We know she has to work on Monday, Wednesday and Thursday so far. If she works on Tuesday, she would be working for 4 consecutive days which is wrong.
Since Amy cannot work on a Tuesday and 2 operators must work on a single day, Bob and Carla must work on a Tuesday.
Therefore, Carla works on Tuesday, Wednesday and Friday.
So the answer is A.