[R] Adding new columns to (output) data - e.g., read 5 cols write 8

[Esmail Bonakdarian]

Hello, I have the following task I'd like to accomplish:

A file contains 5 columns of data (several hundred rows), let's call
them a, b, c, d and e (ie these are their column headers)

I also have a set of definitions, e.g.,

f = a + b
g = a * 3
h = c + d
etc.

I would like to write out a new .rda file that contains columns

a b c d e f g h etc.

I.e. , the original data plus new columns (with headers and data).

It seems that there ought to be a simple way to do this, could
someone provide some guidance on the best way to accomplish
this task? (I tried a few things as this seemed rather trivial,
but did not succeed. I still hope/assume this is a trivial thing
to do if one knows R well)

Thanks,

Esmail

ps: I want to thank everyone again who posted their solutions
     to my previous query. Seeing different solutions for the same
     problem is a tremendously effective way to learn something
     new.