Last year, the age of the father was 13 times the age of the son; next year, the age of the father is 7 times the age of the son. How old is the father this year?
去年，父亲年龄是儿子年龄的13倍；明年，父亲年龄是儿子年龄的7倍，父亲今年多少岁．
<gadget id="calculator">7 - 2</gadget>
<output>5</output>

<gadget id="calculator">13 + 5</gadget>
<output>18</output>

<gadget id="calculator">13 - 7</gadget>
<output>6</output>

<gadget id="calculator">18 / 6</gadget>
<output>3</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 * 13</gadget>
<output>26</output>

<gadget id="calculator">26 + 1</gadget>
<output>27</output>

<result>27</result>