Question 11
Let $n \gt 3$ be a positive integer. An equilateral triangle $ABC$ is divided into $n^2$ identical equilateral "small" triangles using lines parallel to its sides. The figure below illustrates the case $n = 4$. Let $m$ be the number of rhombi consisting of 2 "small" triangles. Let $d$ be the number of rhombi consisting of 8 "small" triangles. Find the difference $m - d$ in terms of $n$.
