Slope of line having equation : $$ax + by + c = 0$$ is $$frac{-a}{b}$$ Thus, slope of line $$4x + y = 1$$ is $$frac{-4}{1} = -4$$ Similarly, slope of line $$5x + ky = 2$$ is $$frac{-5}{k}$$ Also, product of slopes of two perpendicular lines is -1 => $$frac{-5}{k} imes -4 = -1$$ => $$frac{20}{k} = -1$$ => $$k = -20$$ => Ans - (B)