The number of households in a building without broadband accounts for (1/7) of the total number of households. If there are two more households with broadband installed, the number of households without broadband accounts for exactly (1/9) of the total number of households. How many households are there in the building?
一栋楼没安装宽带的户数占居民总户数的(1/7)，如果再有两户装上宽带，没安装宽带的户数恰好占总户数的(1/9)，这栋楼有多少户？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/7) - (1/9)</gadget>
<output>2/63 = around 0.031746</output>

<gadget id="calculator">2 / (2/63)</gadget>
<output>63</output>

<result>63</result>