4. A 30-Volts battery with zero source resistance is connected to a coaxial line of characteristic impedance of 50 Ohms at t = 0 second and terminated in an unknown resistive load. The line length is such that it takes 400 gs for an electromagnetic wave to travel from source end to load end and vice-versa. At t = 400 gs, the voltage at the load end is found to be 40 Volts The steady-state current through the load resistance is