Hey danimalswim.
Hint: |z| = SQRT(x^2 + y^2) if z = (x,y).
The absolute value sign around the "2u-v" means the vector length or magnitude of the vector. This pretty much gives you the scalar value of the vector. It can be found by using the formula that chiro has given you.
Just do the inside 2u-v first before using the formula. Cheers.