Sayid made a chart listing data of two colliding objects. A 5-column table titled Collision: Two Objects Stick Together with 2 rows in the first 3 columns and 1 row in the last 2 columns. The first column labeled Object has entries X, Y. The second column labeled Mass before Collision (kilograms) has entries 300, 100. The third column labeled Velocity before Collision (meters per second) has entries 10, negative 6. The fourth column labeled Mass after Collision (kilograms) has entry 400. The fifth column labeled Velocity after Collision (meters per second) has entry ?. According to the law of conservation of momentum, what is the missing value in the chart?