Suppose 15 states pass a law that limits trial lawyers' compensation. No such law passed in the other 35 states. Suppose that the value of all malpractice suits goes from an average of $2.4 billion to $2.8 billion in those 15 states and goes from $2.3 billion to $2.6 billion in the 35 states over the time in which the laws were passed. What is the difference-in-difference estimator of the effect of these laws