Learn Spanish (Spain): Es importante que resolváis la queja rápido. - It is important that you pl. solve the complaint quickly.

Even though resolver changes its stem from o to ue in most forms, -ar and -er verbs keep their regular stem in the nosotros and vosotros forms of the present subjunctive. Since resolváis is the vosotros form, the o does not change to ue.

Why do we need the subjunctive resolváis here instead of the indicative resolvéis?

The phrase Es importante que is an impersonal expression that expresses an opinion or a value judgment. In Spanish, these expressions always trigger the subjunctive for the verb that follows them, because you are focusing on the idea or importance of the action rather than stating a concrete fact.

Why is rápido used here instead of rápidamente?

In everyday Spanish, it is very common to use certain adjectives, like rápido, as adverbs. You could absolutely say rápidamente here, but using rápido is highly natural and frequent in conversation when talking about doing something fast.

Is the noun la queja related to the verb quejarse?

Yes! The reflexive verb quejarse means to complain, and la queja is its noun form, meaning the complaint.