ORACLE calculate hours between two timestamps [duplicate] - sql

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Closed 11 years ago.
Possible Duplicate:
Calculate difference between 2 date / times in Oracle SQL
so i am creating a database for an airline as part of my university coursework. first time using oracle.
I am trying to calculate the hours between two timestamps.
so something like
v_interval = new.departure_time - v_arrival_time;
v_days = extract (day . v_interval);
v_hours = extract (hours, v_interval) + (v_days * 24);
how do you guys think i should do it?

Similar question:
Calculate difference between 2 date / times in Oracle SQL
More examples:
Date / Time Arithmetic with Oracle 9/10

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This question already has answers here:
Calculate difference between 2 date / times in Oracle SQL
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