A 1.4-kg hawk, traveling west at 15 m/s, seizes a 0.20-kg dove. Just before being seized, the dove was flying east. Just after catching the dove, the hawk's speed is 12 m/s, and it is still moving west. What was the speed of the dove just before it was seized? Note: be careful with signs.
The dove's speed was _____ m/s (enter a positive value).