in which用法These are the days in which it takes two salaries

这里in which 引导的是定语从句,修饰days ,in which 相当于 when ,在从句中作时间状语,不能直接用which ,which 在从句中是充当主语或宾语的.

记住哦，in等介词提前，后面一定用which
These are the days in —which— it takes two salaries for each home,but divorces increase.
in which 不是就=where,只有先行词为地点（包括抽象地点）时才相等。此处先行词为 the days，为时间

which指代这里的先行词the days，in which相当于in the days引导后面的定语从句。
in which表示地点的时候等于where，如果表示时间的话就相当于when。
希望能帮到你，望采纳。