Do distributed property  
7/3+3(2/3-1/3)^2
7/3+3×(2/3-1/3)^2
7/3+3×(1/3)^2
7/3×3×1/9
7/3×1/3
7+1/3
8/3 or 2 and 2/3 or 2.66667
 
        
                    
             
        
        
        
I'm not real sure if this is right but I did my best
        
                    
             
        
        
        
From the problem, the vertex = (0, 0) and the focus = (0, 3)
From the attached graphic, the equation can be expressed as:
(x -h)^2 = 4p (y -k)
where (h, k) are the (x, y) values of the vertex (0, 0)
The "p" value is the difference between the "y" value of the focus and the "y" value of the vertex.
p = 3 -0
p = 3
So, we form the equation
(x -0)^2 = 4 * 3 (y -0)
x^2 = 12y
To put this in proper quadratic equation form, we divide both sides by 12
y = x^2 / 12
Source:
http://www.1728.org/quadr4.htm
 
        
             
        
        
        
The absolute error is 4 cubic inches. To find the absolute error, you simply subtract the two values.
The percent error is 10%. To find the percent error, we create a fraction out of the error and the actual value.
4 / 40 x 100 = 10%