Stocks X and Y are currently priced at $20 and $30 and follow generalized Wiener processes (we will forgive the unrealistic model for now) with drifts of $2 and $3 and standard deviations of $10 and $15 per year respectively. What is the standard deviation per year on a portfolio that holds one share of X and one share of Y if the changes in X and Y over any short interval of time have a correlation of .5?