A tractor plows a piece of land. It plows (3/10) square kilometers on the first day and (7/10) square kilometers on the second day. How many square kilometers is the cultivated land?
一台拖拉机耕一块地，第一天耕了(3/10)平方千米，第二天耕了(7/10)平方千米，两天正好耕了总数的(1/4)，这块耕地共有多少平方千米？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">(3/10) + (7/10)</gadget>
<output>1</output>

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

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

<result>4</result>