After a restaurant paid business tax at a rate of 15% in October, its actual income was 17,850 yuan. How much is the pre-tax income of this restaurant?
一家饭店十月份按照15%的税率交纳了营业税后，实际收入17850元．这个饭店税前的收入是多少元？
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">1 - (3/20)</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">17_850 / (17/20)</gadget>
<output>21_000</output>

<result>21_000</result>