Bubble is 7 years younger than Moomao, and after another 4 years, Bubble's age will be half of Moomao's age, so what is the sum of their ages this year?
泡泡比毛毛小7岁，再过4年泡泡的年龄将是毛毛年龄的一半，那么他们今年的年龄总和是多少岁．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">7 / 1</gadget>
<output>7</output>

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

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

<result>13</result>