Answer: structural unemployment
Explanation: Bob is likely to be without job for a long time as he may need to go back to school and learn the newest techniques. This is because he lacks the technological skills to keep up with the latest equipment (automatic welding machine) that has been installed in the company. This leads to a structural unemployment situation which is defined as unemployment that occurs as a result of a mismatch between the available jobs and the skill levels of the unemployed (Bob). A structural change in the company (installation of an automatic welding machine) has cost Bob his job due to his lack of skill to operate the new machine.