"When did you go to the garage?"
Translation:Pryd est ti i'r garej?
Because Welsh verbs have different forms depending on the person doing the action. "Mynd" is an irregular verbs, and so in this form of the past tense it can be, "Es i" (I went), "Est ti" (You went: inf/sin), "Aeth fo/fe or hi" (He or She went", "Aethon ni" (We went), ""Aethoch chi" (You went: for/plu) and "Aethon nhw" (They went). So the sentence "When did you go to the garage" can be either "Pryd est ti i'r garej" or "Pryd aethoch chi i'r garej", but not "Pryd aeth ti/chi i'r garej" because that is the incorrect conjugation of the verb.