I've had a bunch of these type of problems come up, and I'm at a loss to how to go about solving them. Maybe someone could show me a direction to start in?

http://img715.imageshack.us/img715/7563/136i.png

I know that because the vectors v1 and v2 are parallel, then the dot product of v1 and v2 = 0. But, I'm not sure how to relate that to the problem.

Any help would be appreciated. Thanks!