Answer is C
The conjugate of the complex number a+bi is a-bi 
you just reverse the sign of the imaginary part of the number ; so it is 4-51i 
        
             
        
        
        
Answer:
108ft³
Step-by-step explanation:
V=(base area) (h/3)   =    81 (4
/3) =108ft³
 
        
             
        
        
        
6 √5
7 π
Both continue on forever and will never have an exact answer - therefore, they're irrational.