Draw the Thevinin's equivalent using the voltage from Step 2 and the resistance from Step 4. So the equivalent circuit is a 5V battery with a 15K series resistor. Try computing the voltage delivered to a 50 ohm load without creating a Thevinin model. Speaking of 50 ohms, the Thevinin model can help you understand why matching antennas to transmitters is so important. Remember, power is voltage time current.
Lower resistance makes more current but less voltage.
This is an effect of conservation of energy. The power maximum is at the point where the load and the source are equal. This is why you want 8 ohm speakers on an 8 ohm amplifier output, or a 50 ohm antenna on a transmitter. Assume the transmitter is also a 50 ohm source impedance. That means it's Thevenin voltage is about 140V. Now replace the 50 ohm load with a 10 ohm load.