Question

Let x1, x2,..., x20 be distinct points on the x-axis and let y1, y2,...,y13 be distinct points on the y-axis. For each pair xi, yi, draw the segment connecting xi yo y1. Assume that no three of these segments intersect in one point. How many points of intersection are there? (Don't count intersection points on either of the axes) If you can explain why... it will be awesome cuz i'm trying the best i can.