Misty wants to diversify her exposure and is offered a $1-$year European call Option on oil at strike K$=25$$ for C$=4$$$.$ The current oil price is at S$=20$$ and the $1-$year interest rate is $4\%.$ Using the Put$-$Call$-$Parity, estimate the price of a European put Option on oil with the same strike and maturity. the answer should be $8\mathrm{.}04.$ But what is the calculation behind it$?$