If someone travels from A to B, if he travels 4 kilometers per hour, he will arrive 4 hours later than the scheduled time; if he travels 5 kilometers per hour, he will arrive 3 hours earlier than the scheduled time. Find the distance in kilometers between A and B.
某人从甲地到乙地，如果每小时行4千米，就比预定时间要晚到4小时；如果每小时行5千米，则比预定时间提前3小时到达．求甲、乙两地相距多少千米．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">16 + 15</gadget>
<output>31</output>

<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">31 / 1</gadget>
<output>31</output>

<gadget id="calculator">31 + 4</gadget>
<output>35</output>

<gadget id="calculator">4 * 35</gadget>
<output>140</output>

<result>140</result>