Students of Wenhua Primary School donated books to children in impoverished mountainous areas. The fourth grade donated 435 books, the fifth grade donated twice as much as the fourth grade, the sixth grade donated 105 books less than the sum of fourth and fifth grades, how many books did the sixth grade donate ?
文化小学学生为贫困山区孩子捐书，四年级捐书435本，五年级捐的本数是四年级的2倍，六年级捐的本数比四五年级的总和少105本，六年级捐书多少本？
<gadget id="calculator">435 * 2</gadget>
<output>870</output>

<gadget id="calculator">870 - 105</gadget>
<output>765</output>

<gadget id="calculator">435 + 765</gadget>
<output>1_200</output>

<result>1_200</result>