Find the value(s) of k so that the pair of equations x + 2y = 5 and 3x + ky + 15 = 0

Find the value(s) of k so that the pair of equations x + 2y = 5 and 3x + ky + 15 = 0 has a unique solution.

For unique solution

$$ \frac{1}{3} \ne \frac{2}{k} $$

k ≠ 6