We have already said that the subordinate clause with congiuntivo must be replaced with a construction with the infinitive if the main clause shares the subject with the subordinate clause. (A subordinate clause is not possible in this case and and for this reason the sentence below are marked with an ~.)

Beside that we must see that in this case as well we can distinguish several situations.

The subordinate clause describes the beginning of an action / event.   ~ Prima che ti risponda, devo informarmi.   Prima di risponderti, devo informarmi.   Before I answer you I must inform myself.   The subordinate clause describes the action / event as something hypothetically finished.   ~ Non può uscire prima che abbia fatto i suoi compiti.   Non può uscire prima di aver fatto i suoi compiti.   Before he had not done his homework, he can' t go out.

exercise 8: Transforme the sentences above in a sentence with infinitive ~ Primi che tu scriva, dovresti pensare.    ?  Before writing it would be better to think a bit before.   ~ Prima che fosse arrivato, aveva chiamato.    ?  Before he came, he called me.   ~ Dopo che avrà riparato la macchina, potrà partire.   ?  After having repaired the car, he can leave.