What is the change in the intensity of red light given off by an incandescent body if the temperature increase?

Use Stefan-Boltzmann's Law, in it's simplest form. You can find her somewhere here:

http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

but I think it is something as
P=sigma*T^4,
where P is the power, sigma the stefan-Boltzmann's constant and T temperature.