[closed] How can i combine multiple areas to one big area?

Hey Guys, i have the following problem.

When i do the this querry:

rel(area.niedersaschsen)["boundary"="postal_code"]["postal_code"~"^26"];)->.bereich26;

.bereich26 out geom;

I get all relations, whose postcode starts with 26. Now i want to combine all those single relations to one big area. Can anybody tell if this is possible and if, how can it be realised. Thanks in advance and sorry for my bad english.