Answer
$91.33^{\circ}$
Work Step by Step
We know that the angle between two vectors is:
$\theta =\cos^{-1} [ \dfrac{u \cdot v}{||u|| \space ||v|| }]$
Therefore, $||u||=\sqrt{3^2+4^2}=5$ and $||v||=\sqrt{(-7)^2+(5)^2}=\sqrt {74}$
$\theta =\cos^{-1} [ \dfrac{(3)(-7)+(4)(5)}{ 4\sqrt {13}}]=\cos^{-1}[\dfrac{-1}{5\sqrt{74}}]$
So, $\theta =91.33^{\circ}$
