I hope this helps you 
y=x^2-81
x^2=y+81
x=square root of y+81
f^-1 (x)= square root of x+81
        
                    
             
        
        
        
Well first do you parentheses and the multiply all of your exponets 
        
             
        
        
        
39-(15z+48)/27=35
39-35=(15z+48)/27
4=(15z+48)/27
108=15z+48
108-48=15z
60=15z
z=60/15
z=4
        
             
        
        
        
Let
A------> <span>(5√2,2√3)
B------> </span><span>(√2,2√3)
we know that
</span>the abscissa<span> and the ordinate are respectively the first and second coordinate of a point in a coordinate system</span>
the abscissa is the coordinate x<span>
step 1
find the midpoint
ABx------> midpoint AB in the coordinate x
</span>ABy------> midpoint AB in the coordinate y
<span>
ABx=[5</span>√2+√2]/2------> 6√2/2-----> 3√2
ABy=[2√3+2√3]/2------> 4√3/2-----> 2√3
the midpoint AB is (3√2,2√3)
the answer isthe abscissa of the midpoint of the line segment  is 3√2
see the attached figure
 
        
        
        
Its 2 i guess but im not sure