help solve this. thanks

(4) Let A be an associative algebra. (a) Show that for any a E A the map da : A - A defined by da(b) = ab - ba is a derivation. Such derivations are called inner derivations. (b) Show that inner derivations form an ideal in Der(A). (c) Show that any derviation of the associative algebra A = Mat, (C) of complex n X n matrices is inner