It's difficult to live in a foreign country, ______ if you can't understand the language there.
一项工程，甲单独做需15天完成，乙单独做需20天完成。如果甲做3天后，乙再单独做，还需几天才能完成？
8.62×____＝0.862×11.2
____×24.9＝2490×0.68
