Xiao Ming's home is 3.5 kilometers away from school. Usually he always walks to school. One day he wants to exercise. He runs fast for the first (1/3) distance at 4 times his walking speed, and jogs for the rest of the distance at his walking speed. 2 times, so that he arrives at school 35 minutes earlier than usual, what is Xiao Ming's walking speed?
小明家到学校3.5千米，通常他总是步行上学，有一天他想锻炼，前(1/3)的路程快跑，速度是步行速度的4倍，后一段路程慢跑，速度是步行速度的2倍，这样比平时早35分到校，小明步行速度是多少？
<gadget id="calculator">24.5 / 7</gadget>
<output>3.5</output>

<result>3.5</result>