Build up the equations for high tiles (such as 81 or 90) using the tiles on the rack (such as 9 × 9 = 81, where the player holds the 81 and one or both of the 9s).
To create equations for large tiles (like 81 or 90), use the tiles available on the game board (such as 9 x 9 = 81, where the player has the 81 and either one or both of the 9s).