Staley Co Manufactures Computer Monitors

Staley Co. manufactures computer monitors. The following is a summary of its basic cost and revenue data:Assume that Staley Co. is currently selling 600 computer monitors per month and monthly fixed costs are $80,000.
What is Staley Co.'s margin of safety (MOS) , in units, if 600 units are sold and all costs and revenues are as budgeted? (Round intermediate calculation up to nearest whole number of units.)

A) 123.
B) 242.
C) 128.
D) 141.
E) 214.