Resistance Questions

A material $B$ has twice the specific resistance (resistivity) of $A$. A circular wire made of $B$ has twice the diameter of a wire made of $A$. For the two wires to have the same resistance, the ratio $L_A/L_B$ of their respective lengths must be:

The resistance of a bulb filament is $100\Omega$ at a temperature of $100^{\circ }\text{C}$. If its temperature coefficient of resistance be $0.005$ per ${}^{\circ }\text{C}$, its resistance will become $200\Omega$ at a temperature of: