"☆" means a new operation, which makes the following equations true: 2☆3=8, 4☆2=8, 5☆3=11, 7☆10=27, and calculate according to this rule: 7☆4.
"☆"表示一种新运算，使下列等式成立：2☆3=8，4☆2=8，5☆3=11，7☆10=27，按此规律计算：7☆4．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">7 + 8</gadget>
<output>15</output>

<result>15</result>