Using the put-call parity relationship with discrete compounding: $P + S = C + \frac{K}{(1+r)^t}$. $P = C - S + \frac{K}{(1+r)^t} = 8.50 - 52.00 + \frac{50}{(1.06)^{120/365}} = -43.50 + \frac{50}{1.01937} = -43.50 + 49.05 = 5.55$. The fair value of the put option is USD 5.55. Since it is currently selling for USD 4.00, it is undervalued by $5.55 - 4.00 = 1.55$.