A physics department has just bought a brand new laser for £10000

A physics department has just bought a brand new laser for £10000. It costs £2000, £2700 and £3100 to maintain a laser during its first, second and third year of service respectively. A laser can be sold for £8000, £7000 and £6000 after one, two and three years of use respectively. In four years’ time the department will move to a new campus and will therefore sell the laser. Model this situation as a network optimization problem and solve it using Dynamic Programming. What is the department’s optimal strategy of laser ownership? Assume that lasers can only be bought and sold in August (when staff are on holiday) and that they would always buy a brand new laser. Furthermore assume that a three-year-old laser will always be sold.