Answer: Variable cost
Step-by-step explanation:
The slope of a regression line is meant to represent the change in the total variable or y, as a result of a change in the number of independent observations or x.
The cost that changes during production as a result of an increase in x which is the volume of products, is the variable cost so it is the slope of the total cost line,
Slope of total cost line:
y = mx + c
y = total cost
m = variable cost. m is also slope.
x = production volume
c = fixed cost