12.Sunray Electric lCoop uses a eet of 20 trucks to service its electric network. The company wants to develop a preventive maintenance schedule for the eet. The probability of a breakdown in year 1 is zero. For year 2, the breakdown probability is .03, increasing annually by .l for years 3 through 10. Beyond year 10, the breakdown probability remains constant at .13. The cost per truck is $200 for a random breakdown and $75 for a preventive maintenance. (a) Develop the associated decision tree. (b) Determine the optimal period {in years} between successive preventive maintenances