The equation x+3=10 has the same solution as mx=21, find the value of m.
方程x+3=10与mx=21有相同的解，求m的值．
<gadget id="calculator">10 - 3</gadget>
<output>7</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<result>3</result>