Well you will just subtract 91 - 7 which equals 84. 
So 7 + 84 = 91
        
                    
             
        
        
        
Only multiplication and division don't change the ratio that made the order pairs in the bigger picture the triangle. Only one is not congruent. I'm about 90% sure I got it correct. 
 
        
             
        
        
        
Area of ABC : AB*AC/2
the maximum of the parabola is reached at x=-4/(2*(-1))=2 hence A is at (2,0) and B is at (2,(-2)^2+4*2+C)=(2,12+C)
C is the second root (x-intersect), which we can find :
determinant1 : D=16-4*(-1)*C=4(4+C) thus the second root is at x=

Hence the area of the triangle is 

 hence 

 .
We remark that 

Hence 4+C=16 thus
 C=12