Its a wave that is perfectly reflected upon itself within a medium with negligible absorption.

I need help with this optics problem I have here. Its a wave that is perfectly reflected upon itself within a medium with negligible absorption. I'm told to find the wavelength, amplitude, period, and speed of the resulting composite wave.Now what exactly is a composite wave here? Is there a way you can help me out with this, I could really use the help.I attached the problem itself on here that has the wave function on it, and could probably better explain the problem better. Please help me out