A schoolbag is 48 yuan, a pencil case is 39 yuan cheaper than a schoolbag, and a set of children's books is 28 yuan more expensive than a pencil case. How much is a set of children's books?
一个书包48元，一个文具盒比书包便宜39元，一套儿童图书又比文具盒贵28元．一套儿童图书多少元钱？
<gadget id="calculator">48 - 39</gadget>
<output>9</output>

<gadget id="calculator">9 + 28</gadget>
<output>37</output>

<result>37</result>