The students are doing exercises. Zhao Lei is standing in the 4th row from the left and the 8th row from the right. He is the 5th from the front and the 7th from the back. If the number of students in each row is equal, how many students do the exercises? ．
同学们做操，赵磊站在左起第4行，右起的第8行，从前面数是第5个，从后面数是第7个，如果每一行的人数相等，共有多少名同学做操．
<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">5 + 6</gadget>
<output>11</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">4 + 7</gadget>
<output>11</output>

<gadget id="calculator">11 * 11</gadget>
<output>121</output>

<result>121</result>