Final answer:
The work done in the x-direction is equal to the change in kinetic energy, represented by the equation Wx = ΔK.
Step-by-step explanation:
The work-energy theorem states that the work done on a particle in the x-direction is equal to the change in its kinetic energy. Therefore, the equation for work in the x-direction is represented by the option b) Wx = ΔK. In this equation, Wx represents the work done in the x-direction, and ΔK represents the change in kinetic energy.