A, B, and C have a total of 100 extracurricular books. When A's original number is divided by B's original number, and C's original number is divided by A's original number, the quotient is 5 and the remainder is 1. So how many books does B have?
甲、乙、丙共有100本课外书．甲的本数除以乙的本数，丙的本数除以甲的本数，商都是5，余数也都是1．那么乙有多少本书？
<gadget id="calculator">100 - 7</gadget>
<output>93</output>

<gadget id="calculator">93 / 3</gadget>
<output>31</output>

<result>31</result>