ANSWER:
Prison gangs often engage in "illegal economic activities" like prostitution within the "prison walls".
Step-by-step explanation:
- Prostitution helps the prison gangs to earn extra money in all illegal manner. Prison gangs generally do not get to earn a lot in prison walls.
- These gangs indulge in a variety of activities so that they can earn some money but in an illegal manner.
- The prison gangs also indulge in these illegal economic activities in a secret manner without letting the prison authorities know of the same.