4. (25 Points) When a new delivery truck hits the road, its value starts to diminish. A company invests in a delivery truck for $18,500. After being in service for 2 years, its worth has dropped to $11,500.

a. Using the relationship between time since purchase and value, establish a linear equation to represent the truck's value.

b. Explain the significance of the slope and y-intercept within this scenario.

c. What will the truck's worth be after 4 years of use?

d. Often, firms will offload older vehicles while they retain some resale value, reinvesting the proceeds into newer models. Based on the established equation, how many years will pass before this truck's value drops to $1000?