Now stipulate an operation: a*b=ab+ab, where a and b are rational numbers, what is the value of 3*5
现规定一种运算：a*b=ab+a-b，其中a、b为有理数，则3*5的值为多少
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">3 - 5</gadget>
<output>-2</output>

<gadget id="calculator">15 + (-2)</gadget>
<output>13</output>

<result>13</result>