A ton of coal weighs x tons, 12 tons are transported away, and 23 tons are left. Write the equivalent relationship and list the equations.
一顿煤重x吨，运走12吨，剩23吨，写出等量关系式，列方程．
<gadget id="calculator">23 + 12</gadget>
<output>35</output>

<result>35</result>