Ali is a student at the University. He recently purchased a car for OMR5,000 to use it for going to the University. Ali also expects that other friends might ask for transportation from him. He expects a total monthly revenue of OMR50. He expects fuel cost to be OMR40 per month. One of Ali's friends is a taxi driver. He offered Ali to take him to University for a monthly fee of OMR10. Because he does not have to drive, Ali believes that he can perform online work that would earn him a monthly revenue of OMR10. What is the differential cost in ?this scenario a. OMR10 b. OMR40 c. OMR30 d. OMR20 e. OMR50