"Missing Number Train" is a vibrant, gamified educational interactive application. It introduces the structural foundation of algebra—specifically solving for a single unknown variable (e.g., x + 5 = 12 or 24 - x = 15)—by contextualizing equations as a train journey. In this game, a cute pixel-art locomotive chugs onto the screen pulling a sequence of mathematical cargo beds. One of the beds houses a missing box marked with a question mark (`?`). The student assumes the role of the Station Maste