$((12\frac{1}{2} - 2) : (\frac{1}{5} - \frac{1}{40}) - (2 + 6\frac{2}{3}) : (1\frac{5}{6} - 1\frac{2}{3})) * \frac{3}{8} = (10\frac{1}{2} : \frac{1 * 8 - 1}{40} - 8\frac{2}{3} : (\frac{5}{6} - \frac{2}{3})) * \frac{3}{8} = (\frac{21}{2} : \frac{7}{40} - \frac{26}{3} : \frac{5 - 2 * 2}{6}) * \frac{3}{8} = (\frac{21}{2} * \frac{40}{7} - \frac{26}{3} * \frac{6}{1}) * \frac{3}{8} = (\frac{7 * 3}{2} * \frac{2 * 20}{7} - \frac{26}{3} * \frac{3 * 2}{1}) * \frac{3}{8} = (3 * 20 * 26 * 2) * \frac{3}{8} = (60 - 52) * \frac{3}{8} = 8 * \frac{3}{8} = 3$