B. 4. 
You can get this by setting them equal to each other and getting all of the x terms to one side. Then get the number values to the other and divide the coefficient away. 
        
             
        
        
        
Answer:
a. x=2, y=13
b. x=14, y=25
c. x=−4, y=13
Step-by-step explanation:
 
        
             
        
        
        
No. Quincy should have used the trend line to find the corresponding x value when y=80.