Solve the equation: 9x+4x=12.
解方程：9x+4x=12．
<gadget id="calculator">9 + 4</gadget>
<output>13</output>

<gadget id="calculator">12 / 13</gadget>
<output>12/13 = around 0.923077</output>

<result>12/13 = around 0.923077</result>