Final answer:
The type of unemployment that applies in this situation is structural unemployment, as the shift from horse-drawn carriages to automobiles led to a mismatch between available jobs and the skills of the workers.
Step-by-step explanation:
In this case, the unemployment type that applies to the workers who were laid off when the automobile replaced horse-drawn carriages as the principal means of transportation is structural unemployment. Structural unemployment occurs when there is a shift in the structure of the economy, leading to a mismatch between available jobs and the skills or locations of workers.
In this situation, the firms producing horse-drawn carriages went bankrupt because their product was no longer in demand. As a result, they had to lay off all their workers. The workers who were trained and specialized in making horse-drawn carriages faced difficulty in finding new jobs because their skills were no longer needed.
This is an example of structural unemployment because the workers' unemployment is a result of a structural change in the economy, specifically, the shift from horse-drawn carriages to automobiles as the principal means of transportation.