Xiaodong bought 8 ballpoint pens and 10 exercise books for a total of 18.9 yuan. Each ballpoint pen is 0.8 yuan. How much is each exercise book? (Use equations and arithmetic to solve)
小东买了8枝圆珠笔和10本练习本，共花了18.9元，每枝圆珠笔0.8元，每本练习本多少元？(用方程，算术两种方法解答)
<gadget id="calculator">0.8 * 8</gadget>
<output>6.4</output>

<gadget id="calculator">18.9 - 6.4</gadget>
<output>12.5</output>

<gadget id="calculator">12.5 / 10</gadget>
<output>1.25</output>

<result>1.25</result>