The school is going to distribute exercise books to 15 classes, each class has 142 copies, and the whole school needs to keep 50 copies as spares. How many exercise books should schools buy?
学校准备发练习本，发给15个班，每班142本，全校还需要留50本作为备用．学校应买多少本练习本？
<gadget id="calculator">142 * 15</gadget>
<output>2_130</output>

<gadget id="calculator">2_130 + 50</gadget>
<output>2_180</output>

<result>2_180</result>