Now for Stock Y you first have to calculate Market Sd.. which we know how thanks to rsparks…..but we do not know the Sd of Stock Y itself….But since we are given Sd of X , Covariance bw X and Y , and Correlation bw X and Y we can easily calculate that too!
Correation xy = Covariance xy / sd x * sd y
Just put in the number and you have got sd of stock y!!