Answer:
3 workers
Step-by-step explanation:
It is given that Clara is opening a room cleaning business on the campus. For Clara, there are 5 potential workers.
The daily wage of for the worker are :
Alex ---

Diane --

Cedric --

Peter --

Zekta --

Each of the worker will clean 8 rooms and $ 21 will be charged for each room to be cleaned.
Therefore, the number of the workers required is :
The marginal revenue product for each worker = 21 x 8 = 168
So, Clara will hire only those workers who have daily wage less than $ 168.
Therefore, Clara will hire 3 workers, namely Alex, Diane and Cedric.