A vegetable field, (2/7) is planted with tomatoes, (1/7) is planted with eggplants, how much of this land is left
一块菜地，(2/7)种西红柿，(1/7)种茄子，还剩下这块地多少
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (2/7) - (1/7)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>