We can calculate this problem using this formula: N(p) / N(s) = V(p) / V(s).
Where in the given values are:
N(p) = 600
N(s) = 300
V(s) = 320
V(p) = ?
So;
N(p) / N(s) = V(p) / V(s)
600 / 300 = x / 320 V
192,000 = 300 x
640 = x
This will give us a value of 640 V, which is the input input voltage.