times a number minus the product of 4 and 1.57, the difference is 2.9, what is this number?
一个数的3倍减去4与1.57的积，差是2.9，这个数是多少？
<gadget id="calculator">4 * 1.57</gadget>
<output>6.28</output>

<gadget id="calculator">2.9 + 6.28</gadget>
<output>9.18</output>

<gadget id="calculator">9.18 / 3</gadget>
<output>3.06</output>

<result>3.06</result>