Stock A has an expected rate of return of 12% and a standard deviation of returns of 40%. Stock B has an expected rate of return of 18% and variance of returns of 0.36. The correlation coefficient between the returns of Stock A and Stock B is 0.25. If the risk free rate of return is 6%, then what is the difference in the Sharpe ratio of an optimal (tangent) portfolio and the Sharpe ratio of a minimum risk portfolio, consisting of A and B?