If the solution of mx+6=14 is x=2, find the value of m**2-1.
如果mx+6=14的解是x=2，求m**2-1的值．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">16 - 1</gadget>
<output>15</output>

<result>15</result>