Replying to Physics help

I have a physics final tomorrow, and im having trouble with a couple problems.  any help would be appreciated.


An RLC series circuit has L = 100 mH and C = 1 μF. It is connected to a 1000-Hz source emf is
foundto lead the current by 75°. The value of R is:

The answer is 126 ohms, but i dont know the formula to use.

A soap film is illuminated by white light normal to its surface. The index of refraction of the film is 1.50. Wavelengths of 480 nm and 800 nm and no wavelengths between are be intensified in the reflected beam. The thickness of the film is:

The answer is 4.0 *10^(-5), same thing, I understand the concepts for the most part, but I can't seem to get the right answer.

+++karma for any help