Little Ding Ding was 11 years old last year. This year's father's age is three times that of Xiao Ding Ding's. Grandpa's age this year is four years younger than his father's twice his age. How old is grandpa this year?
小丁丁去年11岁，今年爸爸的年龄是小丁丁的3倍，爷爷今年的年龄比爸爸的年龄的2倍少4岁，爷爷今年几岁？
<gadget id="calculator">11 + 1</gadget>
<output>12</output>

<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">36 * 2</gadget>
<output>72</output>

<gadget id="calculator">72 - 4</gadget>
<output>68</output>

<result>68</result>