Need help in understanding the process for solving the following exercise:

EXERCISE # 4 : Optional : Put - Call Parity : C - P = S - PV ( K ), PV ( K ) = K 1 ( 1 + r ) A - B. The stock is at 50 . One- year interest rates are at 3% . A. A one - year call struck at 52 trades at $4 . What must be the price of a one - year 52 put ? B. A one - year call struck at 50 trades at $5 . What must be the price of a one - year 50 put ?! C . The stock is at 51 . The strike is 55 . A one - year call struck at 51 trades at $4 . A one - year put struck at 55 trades at 1 . 38 . What must be the interest rate ?! 9/0