[R] Normal Distribution Quantiles

[Rainer Schuermann]

This is probably embarrassingly basic, but I have spent quite a few hours in Google and RSeek without getting a clue - probably I'm asking the wrong questions...

There is this guy who has decided to walk through Australia, a total distance of 4000 km. His daily portion (mean) is 40km with an sd of 10 km. I want to calculate the number of days it takes to arrive with 80, 90, 95, 99% probability.
I know how to do this manually, eg. for 95%
$\Phi \left( \frac{4000-40n}{10 \sqrt{n}}  \right) \leq 0.05$
find the z score...

but how would I do this in R? Not qnorm(), but what is it?

Thanks in advance,
and apologies for the level of question...
Rainer