The price of a product is 780 yuan. In order to make small profits but quick turnover, sell at 10% off the selling price and return a 30 yuan gift certificate. At this time, the profit is still 20%. How much is the purchase price of this product?
某商品的售价780元，为了薄利多销，按售价的9折销售再返还30元礼券，此时仍获利20%，此商品的进价是多少元？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">780 * (9/10)</gadget>
<output>702</output>

<gadget id="calculator">702 - 30</gadget>
<output>672</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">672 / (6/5)</gadget>
<output>560</output>

<result>560</result>