The product of 1.5 and 8 is 2.1 less than 3 times of a number. Find this number.
1.5与8的积比一个数的3倍少2.1，求这个数．
<gadget id="calculator">1.5 * 8</gadget>
<output>12</output>

<gadget id="calculator">12 + 2.1</gadget>
<output>14.1</output>

<gadget id="calculator">14.1 / 3</gadget>
<output>4.7</output>

<result>4.7</result>