Most cellphones depreciate (lose value) as they age. A cellphone that costs $1200 will have a value of $520 at the end of 8 years.
a. What is the rate of change of the cellphone’s value with respect to time?

b. Write a formula for its value, V, when it is t years old (for 0
≤t≤

c. Determine the cellphone’s value after 2.5 years. (2 marks)

d. When is the cellphone’s value $800? (2 marks)