。
Let me write you a prescription.
Literal
Medicine [gen-の] prescription [obj-を] make-[favor-てあげる]-[volitional-ましょう].
~てあげる marks the action as a favor done for someone else — the speaker's complementary counterpart of ~てくれる (someone doing for the speaker). Combined with ~ましょう, it becomes 'let me do X for you.' Note that using ~てあげる in actual conversation can sound condescending if overused — it foregrounds the speaker's generosity.