(0.03 * hp)</code>. This means that the marginal effect of weight is large and negative when horsepower is zero (which never occurs in the <code>mtcars</code> dataset) and decreases in magnitude and becoming more positive as horsepower increases. We can see this in the above graph that the marginal effect of weight is constant across levels of <code>weight</code> because <code>wt</code> does not enter into the partial derivative. Across levels, of horsepower, however, the marginal effect becomes more positi