[racket] Extract values from `time` function

Hi,

For benchmarking purposes, I am running a function hundreds of times
and want to make an average of the time it spends running. For that
purpose I am now using `current-inexact-milliseconds` before and after
he loop, and then subtracting both times and dividing by the
iterations performed.

I'd like to do that with the `time` function, but I can't figure out
how to extract the values it prints, since it doesn't seem to be a
return value. I am clearly missing something obvious. How can I use
values returned by `time`?

Thanks a lot,

Sergi