Final answer:
Jim is considered an underemployed worker because he is currently working part-time despite seeking full-time employment, fitting into the category of hidden unemployment.
Step-by-step explanation:
Jim is currently working part-time and is actively seeking full-time employment, making him an underemployed worker. 'Underemployment' is a term used to describe the situation of those who are employed at a lower capacity than their skill set or desired working hours - such as part-time when they would prefer full-time - and are seeking additional or more suitable employment.
This is a part of what's known as hidden unemployment, which also includes discouraged workers who have stopped looking for employment and those with temporary jobs seeking permanent positions. Therefore, the correct classification for Jim's employment situation is b. an underemployed worker.