If  $\alpha ,\beta$  is the orthocentre of the triangle ABC with vertices A (3,-7), B (-1,2) and C (4,5), then  $9\alpha -6\beta +60$  is equal to 

Slope of OA X slope of BC=-1                                    sloer of OB X slper AC=-1
 $\frac{\beta +7}{\alpha -3}\times \frac{3}{5}=-1$                                                         $$\begin{gathered} \frac{\beta -2}{\alpha +1}\times \frac{12}{1}=-1 \\ +12\beta -24=-\alpha -1 \\ \alpha +12\beta -23=0 \end{gathered}$$
     $3\beta +21=-5\alpha +15$
     $5\alpha -3\beta +6=0$