Class 3 and Class 2 were divided into 6 groups and went to the library to read books. There are 30 books left on the shelf. If each group takes 18 books from the shelf, how many books are there on the shelf?
三2班同学分6个小组去图书馆看书后．书架上还剩下30本书，如果每个小组从书架上取走的是18本书，书架上原来有多少本书？
<gadget id="calculator">18 * 6</gadget>
<output>108</output>

<gadget id="calculator">108 + 30</gadget>
<output>138</output>

<result>138</result>