A certain lightbulb has a tungsten filament with a resistance of 21.2 when at 20.0C and 136 when hot.

A certain lightbulb has a tungsten filament with a resistance of 21.2 Ω when at 20.0°C and 136 Ω when hot. Assume the resistivity of tungsten varies linearly with temperature even over the large temperature range involved here. Find the temperature of the hot filament.