Answer
$\theta=143.13°$
Work Step by Step
$\theta=cos^{-1}\frac{u\cdot v}{|u||v|}=cos^{-1}\frac{(3i+4j)(-2j)}{\sqrt {(3i+4j)(3i+4j)}\sqrt {(-2j)(-2j)}}=cos^{-1}\frac{-8}{\sqrt {9+16}\sqrt 4}=cos^{-1}(-\frac{8}{10})=cos^{-1}(-0.8)$
$\theta=143.13°$
