How do I add in date field?

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SQLite

I have a table with following fields:
TABLE dat(a int,dat date,freq int);
I want get a new value in ALIAS column by adding "dat" and "freq" data.

What I have tried:

I want get a new value in ALIAS column by adding "dat" and "freq" data.
I tried in following ways:

select a,dat,freq,date(dat,"+5 Year") as Due_Date from dat;

which working fine result is:

2|2020-01-01|3|2025-01-01

But my object is to add freq value in dat value so i tried as follow:

select a,dat,freq,date(dat,"+freq Year") as Due_Date from dat;

which is not giving result and remain result as:

2|2020-01-01|3

so I need to know how possibly method to get my required result.
Regards