You need to pay 300 yuan to buy three desk lamps and one socket; you need to pay 200 yuan to buy one desk lamp and three sockets. So how much does it cost to buy a desk lamp and a socket.
买三盏台灯和一个插座需付300元；买一盏台灯和三个插座需付200元．那么买一盏台灯和一个插座需付多少元．
<gadget id="calculator">300 + 200</gadget>
<output>500</output>

<gadget id="calculator">500 / 4</gadget>
<output>125</output>

<result>125</result>