MathNet 2010 — Part 05 Question 23

Given an integer number $n \ge 2$, a positive real number $A$, and $n+1$ distinct points in the plane, $X_0, X_1, \dots, X_n$, show that the number of triangles $X_0X_iX_j$ of area $A$ does not exceed $4n\sqrt{n}$.