For what value of $k$ does the system $2x + 3y = 6$, $kx + 6y = 7$ have no unique solution?

Explanation

1. 01

   A unique solution needs $|A| \ne 0$, so there is none when $|A| = 0$: $2(6) - 3k = 0$.

2. 02

   So $k = 4$.