The answer in the blank is counting
        
             
        
        
        
There are 5 letters
there are 5 possibilities for the first letter, and 4 possibilities for the second letter after the first letter is used up
so 5 * 4 = 20 possibilities
        
                    
             
        
        
        
M=2,000÷((1−(1+0.072÷12)^(−12
×2))÷(0.072÷12))
M=89.73