Finding original signal, given signal obtained by sampling

[Jd303]

Let, x(n) = 3.9 cos(0.80πn + 0.2π) be the discrete-time signal obtained by sampling a continuous-time signal x(t) at a sampling rate of 578.4 samples/sec. Find possible expressions for x(t).

Hey all,
I am quiet unfamiliar with this type of question, and haven't been able to put anything together that makes sense.
I know that the amplitude and phase will stay the same, however figuring out possible frequencies has got me stuck. Would greatly appreciate anyone that is able to walk me through or point me in the right direction for this problem. Thanks in advance!

 

[Jd303]

Just had a breakthrough, needed to get away from the problem and then look at it again.
Just in case anyone wants to correct me:
-2*pi*fo/fs = 0.8*pi
-Therefore fo = 231.36
-Therfore possible frequencies are fo +-fs*k where k is an integer