The similarity between the social system is the hierarchy that created in society based on the job that held by individuals.
The main difference is the openness. South Asian culture directly acknowledge the discrimination while the European culture masked it even though the nobles held all the power in the society.
The developing countries are cheaper for production and labor so it is economically beneficial
Here you go. The answer is r = c/ pi. Simply divide both side by pi, in order to isolate the variable r.