Explanation

(c)
$\because a_{1}a_{2} + b_{1}b_{2} = 3(12) + ( - 4)(5) = 16 > 0$
$\therefore$ The equation of bisector of the acute angle between these lines are
$\frac{3x - 4y + 7}{\sqrt{3^{2} + 4^{2}}} = \frac{12x + 5y - 2}{\sqrt{12^{2} + 5^{2}}}$
$\Rightarrow \ 13(3x - 4y + 7) = 5(12x + 5y - 2)$
$\Rightarrow \ 21x + 77y - 101 = 0$