SQLite, how to use expression in datetime modifier

Question

In short: I need to calculate the ending datetime given starting time and length in minutes.

I have a table with columns StartTime (type datetime) and LengthMinutes (type int). To calculate the ending time I would need some sql like this:

select datetime(StartTime, '+LengthMinutes minutes') from my_table;

How do I refer to the column LengthMinutes from within the modifier?

Edited: solved using dan04's suggestion. Thanks!

Answer 1

SELECT datetime(StartTime, '+' || LengthMinutes || ' minutes') FROM my_table;

Answer 2

select datetime(strftime('%s',StartTime)+lengthMinutes*60,'unixepoch') from my_table;