We consider a Black-Scholes model for the price (X),20 of a risky asset, with continuous interest rate r = 0.04 per year, expected return / = 0.05 per year, volatility o = 0.3 year /2 , and we take Xo = 100 Gils We look at a vertical spread with calls: it is a portfolio which is long a European call with strike ] and short European call with strike K