Keeping c subscript 2 constant at c subscript 2 equals 12, the interval for c subscript 1 in which the current optimal solution remains optimal is a. negative 14 less or equal than c subscript 1 less or equal than negative 24 b. 14 less or equal than c subscript 1 less or equal than 24 c. negative 24 less or equal than c subscript 1 less or equal than negative 14 d. 24 less or equal than c subscript 1 less or equal than 14 e. none of the above