It is known that the solution of the equation mx-18=12 is x=4, so what is m=?
已知方程mx-18=12的解是x=4，那么m=多少．
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">30 / 4</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>