The following report for a collision of two marbles has an error. "Marble 1 has a mass of 12 g, an initial speed of 0.84 m/s left, and a final speed of 0.21 m/s right. Marble 2 has a mass of 23 g, an initial speed of 0.42 m/s right, and a final speed of 0.31 m/s left." What change to the report's data would give a correct verification of momentum conservation?