Answer:
Hey the answer is = 24x 
Step-by-step explanation:
An algebraic expression comprises both numbers and variables together with at least one arithmetic operation. To evaluate an algebraic expression you have to substitute each variable with a number and perform the operations included.
HOPE THIS HELPS!
 
        
                    
             
        
        
        
Answer:

Step-by-step explanation:
Assuming that the patio is a rectangle, we have 

Where 
 is the length and 
 is the width.
Now let's assume that the length of the patio is double than the width.

So, the equation that represents this problem is

 
        
             
        
        
        
20( -1.5r + 0.75) 
Multiply everything by 20
= -30r + 15
        
                    
             
        
        
        
56^1 is a easy way to do a exponent I think