A seventh-grade student went to the beach during the winter vacation. When arranging accommodation, if 3 people live in one room, 9 people will have nowhere to live. If 4 people live in one room, there will be an empty room. Question: What is the cost of going to the beach? How many students are there?
某七年级学生在寒假去海滨旅游，在安排住宿时，如果安排3人住一间，则有9人无处住，如果4人住一间，则空一间房，问：去海滨旅游的学生共有几人？
<gadget id="calculator">9 + 4</gadget>
<output>13</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">13 / 1</gadget>
<output>13</output>

<gadget id="calculator">13 - 1</gadget>
<output>12</output>

<gadget id="calculator">4 * 12</gadget>
<output>48</output>

<result>48</result>