1. Sudoku is a game played on a 9x9 board, in which each column, each row, and each of the nine 3x3 subboards must contain all numbers 19 exactly once. What is the asymptotic running time of an algorithm that enumerates all possible Sudoku boards that satisfy these constraints?

2. A train leaves Chicago at 4:20pm and travels south at 25 miles per hour. Another train leaves New Orleans at 1:23pm and travels north at 50 miles per hour. The conductors of both trains are playing a game of chess over the phone. After each player moves, the other player must move before their train has traveled 5 miles. In asymptotic notation, how many moves do the two players make before their trains pass each other (somewhere near Memphis)?