There are 80 white pieces and 50 black pieces in the box. Each time 3 white pieces are taken away and 3 black pieces are put in at the same time, after how many times of taking and placing like this, the white pieces are exactly equal to the black pieces?
盒子里有80枚白子和50枚黑子．每次取走3枚白子，同时放入3枚黑子，像这样取放多少次后，白子与黑子正好相等？
<gadget id="calculator">80 - 50</gadget>
<output>30</output>

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<result>5</result>