\[\boxed{\text{880\ (880).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[y = kx - 15\ \ \]
\[\text{B\ }(3;\ - 6):\]
\[k \cdot 3 - 15 = - 6\ \ \]
\[3k = 9,\ \ \]
\[k = 3\]
\[Ответ:k = 3.\]