The school recently bought 4 computer desks and a chair for a total of 690 yuan. 90 yuan per chair, how much is each computer desk? (column equation solution)
学校最近买了4张电脑桌和一把椅子，共花去690元．每把椅子90元，每张电脑桌多少元？(列方程解答)
<gadget id="calculator">690 - 90</gadget>
<output>600</output>

<gadget id="calculator">600 / 4</gadget>
<output>150</output>

<result>150</result>