 <translate> Give the step-by-step reasoning process and then the final answer. Cameron is printing her thesis in the school library and has 400 A4 pieces of paper. If 40% of the papers did not print out up to her desired quality and she separated them as invalid, calculate the total number of valid documents. <yor> Ṣàlàyé bí wọ́n ṣe ń ronú lẹ́ẹ̀kan-lẹ́ẹ̀kan, kó o sì wá sọ ìdáhùn tó o máa fún wọn. Cameron ń tẹ ìwé ìkẹ́kọ̀ọ́ rẹ̀ jáde ní ibi ìkówèésí iléèwé, ó sì ní irínwó [400] ìwé A4. Bí ìdá ogójì nínú ọgọ́rùn-ún àwọn ìwé náà kò bá tẹ̀ jáde ní irú ẹ̀kúnrẹ́rẹ́ tí ó fẹ́, tí ó sì yà wọ́n sí ọ̀tọ̀ gẹ́gẹ́ bí èyí tí kò lẹ́sẹ̀ nílẹ̀, ṣírò iye ìwé tó lẹ́sẹ̀ nílẹ̀. 