N4 — outside your level filter
write + it's the rule that
kaku koto ni natte iru
it's the rule that; is set to — an arrangement in force, settled by someone other than the speaker
meaning: it's the rule to write
このマンションでは、ごみは朝八時までに出すことになっている。
kono manshon de wa, gomi wa asa hachiji made ni dasu koto ni natte iru.
In this building, it's the rule to put out the rubbish by eight in the morning. neutral
会議は三時から始まることになっています。
kaigi wa sanji kara hajimaru koto ni natte imasu.
The meeting is set to start at three. neutral