We are asked to find the voltage that must be applied to a 6.4 ohm lamp filament to develop a current of 20 amperes.
Recall that Ohm's law is given by
[tex]V=IR[/tex]Where V is the voltage, I is current, and R is the resistance.
Substitute the given values
[tex]\begin{gathered} V=20\times6.4 \\ V=128\; \text{volts} \end{gathered}[/tex]Therefore, a voltage of 128 volts must be applied.
