There are a total of 210 red and white balls in the box. If one red ball and three white balls are taken out each time, when the white balls are taken out, there are still 50 red balls left. How many red balls are there in this box?
盒子里有红、白球共210个，若每次拿出1个红球和3个白球，当白球拿完时，红球还剩50个，那么这盒有红球多少个．
<gadget id="calculator">210 - 50</gadget>
<output>160</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

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

<gadget id="calculator">160 * (1/4)</gadget>
<output>40</output>

<gadget id="calculator">40 + 50</gadget>
<output>90</output>

<result>90</result>