Subject: mathqa
Question: the average salary per head of the entire staff of an office including the officers and clerks is rs . 90 . the average salary of officers is rs . 500 and that of the clerks is rs . 84 . if the number of officers is 2 , find the number of officers in the office ?
Option: 
A: 720
B: 1020
C: 820
D: 620
Answer: C