simple sql commands

please check attached tables i need this for my studies i have a lot more very similar work i need following sql commands 1. select average amoung as AVG_Anzahl that 1 person has i have no idea here 2. select all konto as anzahl where min 1 buchung was performed my attempt: select count(*) as anzahl from konto inner join buchung on [login to view URL] = [login to view URL] but its wrong it gives me 30 instead of 12 the next 3 i also dont know 3. select name and gebdat (date of birth) where konto saldo > 10000 4. select all buchungen where transferred amount ist greater than 1.5 * avg of all 5. select all buchungen where affected inhaber (person) is older than 30 year = 360 months affected means it can be vonkonto (fromaccount) and aufkonto (tooaccount) use SYSDATE and ADD_MONTHS(d,m) for this task transaltion inhaber = person anzahl = amount konto = bankaccount buchung = account transaction