Solution:

Concept: Average speed for two equal distance segments is \( v_{avg} = \frac{2v_1 v_2}{v_1 + v_2} \). Given \( v_{avg} = 48 \text{ km/h} \), \( v_1 = 40 \text{ km/h} \), and \( v_2 = v \). Substitute these values: \( 48 = \frac{2 \times 40 \times v}{40 + v} \). Simplify and solve for \( v \): \( 48(40+v) = 80v \) leads to \( 32v = 1920 \), so \( v = 60 \text{ km/h} \).