The train station clock runs too fast and gain 11 minutes every 3 days. how many minutes and seconds will it have gained at the end of 5 days

In every 3 days, it gains = 11 min = 660 sec
So, In 1 day, it gains = 660/3 = 220 sec.

Now, For 5 days, it would be: = 220 × 5 = 1100 sec
We Know, 1 min = 60 sec. 
So, 1100 sec = 18 1/3 min.

So, Your Final Answer would be 18 min. 20 sec

Hope this helps!