Answer:
Independent Variable
"The longer a U.S. line worker has been employed at a U.S.-based assembly plant..."
Explanation:
The independent variable is the element or variable that is independent of another variable. Â In this case, "how difficult it is for the line worker to find new employment when the assembly plant moves to Mexico" a dependent variable, which depends on the length of time that the "U.S. line worker has been employed at a U.S.-based assembly plant," and not vice versa.