Final answer:
To adjust a manual slack adjuster, the typical direction to tighten is clockwise, while to loosen is counterclockwise. The same directional convention applies when using a wrench, as turning clockwise tightens a nut. The positive direction in a conventional coordinate system is typically forward and to the right.
Step-by-step explanation:
The correct direction for adjusting a manual slack adjuster is not explicitly stated in your question, but generally when adjusting components like a slack adjuster, the direction for tightening is usually clockwise, and to loosen would be counterclockwise. This is similar to the concept shown in Figure 2.31 where a wrench is used to apply torque to a nut; clockwise tightens and counterclockwise loosens. In the context of gears, as mentioned in another portion of your references, when force is applied through gear A, which turns clockwise, it meshes with gear B that turns counterclockwise, affecting its angular velocity.
As for the conventional signs of axes, typically, the direction that is considered positive is forward and to the right, aligning with the traditional Cartesian coordinate system. Therefore, the conventional positive axes as per the provided reference would be option c.