Xiao Ming goes to the stationery store to buy 4 exercise books and a ballpoint pen. The unit price of the ballpoint pen is 1.50 yuan, and the total cost is 3.90 yuan. How much is each exercise book? (Solution problems of column equations)
小明到文具店买4本练习本和一枝圆珠笔，圆珠笔单价是1.50元，一共花了3.90元，每本练习本多少元？(列方程解应用题)
<gadget id="calculator">3.9 - 1.5</gadget>
<output>2.4</output>

<gadget id="calculator">2.4 / 4</gadget>
<output>0.6</output>

<result>0.6</result>