find the required value by setting up the general equation and then evaluating.
find y when x=10 if y varies directly as x and y=20 when x=8
Icemanfan, hope you don't mind me just adding something.
mamajen, In the other question you asked, I said what "proportional" mean and told you about putting the k there and then working out what k was. Well, "varies directly as" just means "is proportional to", so the two questions are quite similar.