The correct answer is $\boxed{\text{D}}$.
The slope coefficient is a measure of the relationship between two variables. In this case, the slope coefficient is 0.60, which means that for every 1 unit increase in machine hours, there is a 0.60 unit increase in cost. The difference in machine hours is 50000, so the difference in cost is 0.60 * 50000 = $30,000. However, this is just the linear relationship between the two variables. There may be other factors that affect cost, such as the type of machine used, the experience of the operator, and the cost of materials. Therefore, the actual difference in cost could be more or less than $30,000.
Option A is incorrect because it is the square of the slope coefficient. The square of the slope coefficient is a measure of the variance of the data points around the line of best fit. In this case, the square of the slope coefficient is 0.36, which means that the data points are relatively spread out around the line of best fit. This suggests that there is a lot of variability in the data, and that the actual difference in cost could be significantly different from $68,700.
Option B is incorrect because it is the product of the slope coefficient and the difference in machine hours. The product of the slope coefficient and the difference in machine hours is a measure of the change in cost for a unit change in machine hours. In this case, the product of the slope coefficient and the difference in machine hours is 0.60 * 50000 = $30,000. However, this is just the linear relationship between the two variables. There may be other factors that affect cost, such as the type of machine used, the experience of the operator, and the cost of materials. Therefore, the actual difference in cost could be more or less than $30,000.
Option C is incorrect because it is the difference in machine hours divided by the slope coefficient. The difference in machine hours divided by the slope coefficient is a measure of the change in cost for a unit change in machine hours. In this case, the difference in machine hours divided by the slope coefficient is 50000 / 0.60 = $83,333.34. However, this is just the linear relationship between the two variables. There may be other factors that affect cost, such as the type of machine used, the experience of the operator, and the cost of materials. Therefore, the actual difference in cost could be more or less than $83,333.34.