Solution and Explanation:
The following method will be used 
The total cost of the firm = 10 multiply with 200 = $2,000 
The Profit per client = $400 
Let x be the no of clients required for break even. At break-even point, 
The total profit = The total cost 
 400x = 2,000, The value of x is to be calculated 
 We get, x = 2,000 divided by 400 = 5 clients 
Hence, secretary should arrange 5 clients to break even.