To tackle this problem, you will be using one theorem: the DOT product of two vectors equals to the product of their magnitudes and the cosine of their angle.
DOT(u,v) = |u| * |v| * Cos(θ)
I won't provide numbers here, but include essential steps for you to move forward:
- Calculate the magnitude of vector u and v: |u|, |v|, which you should know how or Google.
- Calculate the dot product of u and v: DOT(u,v) = u1*v1 + u2*v2 + u3*v3, where u1 etc. are the components of the vectors, eg. u1=7
- Calculate Cos(θ), and then θ using your calculator.