If the current flowing through a resistor is tripled, how many times will the diameter of that resistor increase from the current when the voltage across that resistor remains unchanged?
If you triple the current and the voltage stays the same, the resistance is
i.e. the resistance is reduced by 1/3
For the resistance to be reduced by 1/3, the cross-sectional area must be increased
Therefore, in the cross-sectional area
Since R is reduced by 1/3
This will increase the cross-sectional area by three times.