Sphere W (with an initial charge of zero) is touched to sphere A and then they are separated. Next, sphere W is touched to sphere B (with an initial charge of -29e) and then they are separated. Finally sphere W is touched to sphere C (with an initial charge of +60e), and then they are separated. The final charge on sphere W is +23e. If the initial charge on sphere A was ce, what is the value of c?