There are 180 books in total between class six ① and class six ②. If class six ① gives 30 books to class six ②, the ratio of the number of books between class six ① and class six ② is 4:5. How many books did Class 6 originally have?
六①班和六②班共有图书180本，如果六①班给六②班30本，则六①班和六②班图书数量的比是4：5．六②班原来有多少本图书？
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">180 * (5/9)</gadget>
<output>100</output>

<gadget id="calculator">100 - 30</gadget>
<output>70</output>

<result>70</result>