The first squadron and the second squadron of the fifth grade will go on a spring outing 20 kilometers away from the school. The first squadron walks 4 kilometers per hour, and the second squadron rides bicycles at 12 kilometers per hour. Two hours after the first squadron set off, the second squadron set off again. How many hours did the second squadron catch up with the first squadron?
五年级一中队和二中队要到距学校20千米的地方去春游．第一中队步行每小时行4千米，第二中队骑自行车，每小时行12千米．第一中队先出发2小时后，第二中队再出发，第二中队出发后几小时才能追上一中队？
<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<gadget id="calculator">2 / 8</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">4 * (1/4)</gadget>
<output>1</output>

<result>1</result>