Given that 5x+0.4=1.8 and mx-3=1.2 have the same solution, find the value of m.
已知5x+0.4=1.8与mx-3=1.2的解相同，求m的值．
<gadget id="calculator">1.2 + 3</gadget>
<output>4.2</output>

<gadget id="calculator">1.8 - 0.4</gadget>
<output>1.4</output>

<gadget id="calculator">1.4 / 5</gadget>
<output>0.28</output>

<gadget id="calculator">4.2 / 0.28</gadget>
<output>15</output>

<result>15</result>