Answer:
It will take the apprentice 24 days working alone
Explanation:
Let the number of days it takes the apprentice be x
It will take the landscaper x/3 ( since he is three times faster)
The rate for both will be 60/6 = 10 sq m per day
Rate for apprentice is 60/x
rate for the boss is 60/x/3 = 180/x
Adding the rates together;
60/x + 180/x = 10
240/x = 10
240 = 10x
x = 240/10
x = 24 days