Average Speed = Total Distance &divide; Total Time.<br><br>&bull; Total distance = t + t = 2t m (to school and back)<br>&bull; Total time = 10 + 15 = 25 min<br>&bull; Average speed = \( \frac{2t}{25} \) m/min<br><br>Final Answer: A: \( \frac{2t}{25} \)