The orthocentre of triangle formed by lines xy+3x+3y+9 = 0 and the line 3x+4y–5=0 is

$\mathrm{a}+\mathrm{b}=0\Rightarrow$given pair of  lines are perpendicular to each other.

orthocentre is point of intersection of perpendicular pair of lines

$\mathrm{xy}+3\mathrm{x}+3\mathrm{y}+9=0\Rightarrow (\mathrm{x}+3)(\mathrm{y}+3)=0\Rightarrow \mathrm{x}=-3,\mathrm{y}=-3\Rightarrow 0=(-3,-3)$