To find the midpoint of the line segment \( \overline{AB} \), the formula is:
\[ \text{Midpoint} = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2} \right) \]
From the information provided, it seems Fernando is incorrectly calculating the x-coordinate of the midpoint.
If he has already calculated \( 6.4 + (-2.5) = 3.9 \), that indicates he is adding the x-coordinates of points A and B. The next step should be to divide that result by 2 to find the average. However, it appears he has incorrectly calculated \( 6.4 + (-2.5) \) without including the division by 2.
Therefore, the most appropriate response is:
Fernando should divide 3.9 by 2, then repeat both steps using the y-values.