The sum of 28 and 6.2 minus three times a number equals 15.75. What is this number?
28与6.2的和减去一个数的3倍等于15.75，这个数是多少？
<gadget id="calculator">6.2 - 15.75</gadget>
<output>-9.55</output>

<gadget id="calculator">28 + (-9.55)</gadget>
<output>18.45</output>

<gadget id="calculator">18.45 / 3</gadget>
<output>6.15</output>

<result>6.15</result>