Important information about Finding expressions for the partial molar volumes at T and P

The molar volume (cm^3 mol^-1) of a binary liquid mixture at T and P is given by: V = 120x1 + 70x2 + (15x1 + 8x2)x1x2 (a) Find expressions for the partial molar volumes of species 1 and 2 at T and P. (e)Plot values of V, partial V1, and partial V2 calculated by the given equation for V and by the equations developed in (a) vs. x1. Label points V1, V2, partial V1 infinity, partial V2 infinity, and show their values. I don't know where to start on this. The instructor says that this is a Redlich-Kiester expansion where they've fit an excess molar volume? Like, 120 is the pure molar volume for x1 and 70 is the pure molar volume for x2. The partial V1 infinity and partial V2 infinity means 'infinitely dilute' at x1 and infinitely dilute at x2 respectively. So that, for example, partial V2 infinity at x2=0 means x1=1.0.