Answer:

Step-by-step explanation:
In order to add or subtract numbers in scientific notation, the powers of ten must have the same exponent.  In this caes the diameter of an average human body cell is a power of -4 and the diameter of a plant cell is a power of -3.  In order to add them, we can move the decimal over for the body cell diameter: 

Add the two values: 
 
        
                    
             
        
        
        
45x+6 is the answer
Simply
Subtract the numbers
45x-3(4-6)
45x-3(-2)
Multiply the numbers 
Solution
45x+6
        
                    
             
        
        
        
4136/8= 517
The others
7116/8=889.5
4309/8=538.625
9406/8=1175.75
        
                    
             
        
        
        
Only one time...............