\[y = kx + b;\ \ A(0; - 6);\ \ B(3;0).\]
\[A(0;\ - 6):\]
\[- 6 = 0k + b\]
\[b = - 6.\]
\[B(3;0);\ \ b = - 6:\]
\[0 = 3k - 6\]
\[3k = 6\]
\[k = 2.\]
\[Ответ:k = 2;\ \ b = - 6.\]