The conventional method to do is to of course start calculating ->
=(385-320)*100/320
=65*100/320
=20.3%
Hence 20%
However, this is too time consuming . If you look closely this percentage is basically 60/300 , which is ~20% .
So you can straight away eliminate A,D,E .
We are now left with 17% and 20% . Now we will need to be a bit precise, but still is very doable for those with good mental maths.
=65*5= 325 which is higher than 320. Hence,
=(65/325)*100 = 100/5 =20%
But we need to find 65/320 which will be a bit higher than 20%. Hence we can safely rule out 17%.
Answer is 20%.