A is 7 years younger than B, and A's age will be half of B's in 4 years. What is the sum of their current ages?
A比B小7岁，再过4年A的年龄将是B的一半，他们现在的年龄总和是多少岁．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">4 - 8</gadget>
<output>-4</output>

<gadget id="calculator">7 + (-4)</gadget>
<output>3</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">3 + 7 + 3</gadget>
<output>13</output>

<result>13</result>