There are 54 students in Class 1 of the fourth grade. There are 13 people who subscribe to "Excellent Composition for Primary School Students" and "Mathematics World". There are 45 people who subscribe to "Excellent Composition for Primary School Students". How many people are there in Big World.
四年级一班有54人，订阅《小学生优秀作文》和《数学大世界》两种读物的有13人，订阅《小学生优秀作文》的有45人，每人至少订阅一种读物，订阅《数学大世界》的有多少人．
<gadget id="calculator">54 - 45</gadget>
<output>9</output>

<gadget id="calculator">9 + 13</gadget>
<output>22</output>

<result>22</result>