An optical shop buys a batch of spectacle frames and sells 20 pairs at a retail price of 50 yuan each, which is as much profit as selling 30 pairs at a retail price of 45 yuan. How much is the purchase price of this batch of spectacle frames?
某眼镜店购进一批眼镜架，以零售价每副50元卖出20副，与以零售价45元卖出30副的利润一样多．这批眼镜架的进货价每副多少元？
<gadget id="calculator">45 * 30</gadget>
<output>1_350</output>

<gadget id="calculator">50 * 20</gadget>
<output>1_000</output>

<gadget id="calculator">0 - 1_000</gadget>
<output>-1_000</output>

<gadget id="calculator">1_350 + (-1_000)</gadget>
<output>350</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">350 / 10</gadget>
<output>35</output>

<result>35</result>