Find the Magnitude $\mathbf { u } = \langle 3,4 \rangle$

Multiple Choice

Find the magnitude.
-Let $\mathbf { u } = \langle 3,4 \rangle$ . Find the magnitude (length) of the vector: $- 3 \mathbf { u }$ .

A) 75
B) $- 15 \sqrt { 5 }$
C) 15
D) $- 15$