After how many years were the lands resurveyed and revenue rates increased in the 'Ryotwari System' during the colonial period in India?

30 years

The correct answer is Option 3 - 30 years

Unlike the Bengal system, the revenue was directly settled with the ryot. In the Ryotwari system, the average income from different types of soil was estimated, the revenue-paying capacity of the ryot was assessed and a proportion of it was fixed as the share of the state. The lands were resurveyed every 30 years and the revenue rates increased. Therefore the revenue demand was no longer permanent.