Which Bohr orbit does the electron occupy in this atom?

[map7s]

Homework Statement

he potential energy of a hydrogen atom in a particular Bohr orbit is -2.72 10-19 J.
(a) Which Bohr orbit does the electron occupy in this atom?
(b) Suppose the electron moves away from the nucleus to the next higher Bohr orbit. Does the potential energy of the atom increase, decrease, or stay the same?
(c) Calculate the potential energy of the atom for the orbit referred to in part (b).

Homework Equations

U=-ke^2/r
r=n^2 r
U=-ke^2/(n^2 r)

The Attempt at a Solution

I tried plugging in my numbers into the first equation and solving for r, but I got a really weird number with a very large negative exponent. I then tried plugging the numbers into the third equation (which is just a combination of the first two equations), and I got another really weird number. Am I not supposed to be using these equations?

 

[Astronuc]

Take a look at this and see if something comes to mind.

http://hyperphysics.phy-astr.gsu.edu/hbase/bohr.html#c4