Equal source and load resistances split voltage and dissipated power in this resistive model. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Equal resistances split the source voltage
The source resistance and load are both 4 ohm, so the load voltage is 6 volts.
VL=6V
The two resistors dissipate equal power
The load power is 9 watts, and the source resistor power is also 9 watts. This lesson claims equal splitting, not a maximum proof.