1. The problem asks for the direction of $t$ for particles A and B. 2. Typically, $t$ represents time, which moves forward in the positive direction. 3. For particles, the direction of $t$ is usually along the path of motion as time increases. 4. Without specific information about particles A and B's motion, we assume $t$ increases forward in time. 5. Therefore, the direction of $t$ for both particles A and B is forward in time, from past to future.