The saplings were planted on both sides of the school gate. The original plan was to plant 7 trees on both sides, one tree every 4 meters, but actually 9 trees were planted on both sides. What is the distance between every two trees?
校门口两侧种树苗，原打算两侧都种7棵，每隔4米种一棵，实际两侧都种了9棵，每两棵树间的距离是多少？
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">4 / 8</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">6 * (1/2)</gadget>
<output>3</output>

<result>3</result>