need help with this

A molecule M binds reversibly to a protein receptor R on the surface of a cell. You start with a total concentration of protein receptor [R]o and a total concentration of molecule [M]o. a) (20 points) Assume that the concentration of unbound protein receptor is approximately equal to the total concentration of protein receptor. Develop an expression for the fraction of protein receptors bound by the molecule at equilibrium. Your answer should be in terms of knowns ([M]o, [R]o, and any rate or equilibrium constants). b) (15 points) Now relax the assumption from part (a). Develop a new expression for the fraction of protein receptors bound by the molecule at equilibrium. Your answer should be in terms of knowns ([M]o, [R]o, and any rate or equilibrium constants).