\[\boxed{\mathbf{781}\mathbf{.}}\]
\[(kx + b)^{'} = k.\]
\[1)\ f(x) = 4x = 4x + 0\]
\[f^{'}(x) = (4x + 0)^{'} = 4.\]
\[2)\ f(x) = - 7x + 5\]
\[f^{'}(x) = ( - 7x + 5)^{'} = - 7.\]
\[3)\ f(x) = - 5x - 7\]
\[f^{'}(x) = ( - 5x - 7)^{'} = - 5.\]