\[y = kx + b;\ \ M(0; - 12);\ \ K( - 3;0).\]
\[M(0;\ - 12)\]
\[- 12 = 0k + b\]
\[b = - 12.\]
\[K( - 3;0);\ \ b = - 12:\]
\[0 = - 3k - 12\]
\[- 3k = 12\]
\[k = - 4.\]
\[Ответ:k = - 4;\ \ b = - 12.\]