The distance between A and B is 320 kilometers. The two cars depart from the two cities at the same time and drive towards each other. After 4 hours, the two cars meet. It is known that the speed of the express train is 10 kilometers less than twice the speed of the slow train. Find the slow train speed. (solution by equation)
甲、乙两城相距320千米，两车分别从两城同时出发，相向而行，出发4小时后两车相遇，已知快车的速度比慢车的速度的2倍少10千米，求慢车的速度．(用方程解)
<gadget id="calculator">320 / 4</gadget>
<output>80</output>

<gadget id="calculator">10 + 80</gadget>
<output>90</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">90 / 3</gadget>
<output>30</output>

<result>30</result>