TB MC Qu$.6$A$-7($Static$)$ In describing the cost...

In describing the cost formula equation, $Y=a+bx,$ which of the following is correct:

Multiple Choice

$"$a$"$ and $"$b$"$ are valid for all levels of activity.

in the high$-$low method, $"b"$ equals the change in cost divided by the change in activity.

$"$Y$"$ is the independent variable.

$"a"$ is the variable cost per unit.