Explanation

(b)
Given equation of pair of lines can be written as
$(3x - y)(x + 2y) = 0$
Slope of separate equations of line $3x - y = 0$ is 3 and $x + 2y = 0$ is $- \frac{1}{2}$
$Thus,\ required\ sum = 3 - \frac{1}{2} = \frac{5}{2}$
Alternate
Sum of slope of the lines $3x^{2} + 5xy - 2y^{2} = 0$ is
$m_{1} + m_{2} = - \frac{h}{b} = \frac{5}{2}$