Answer
(a) $75$
(b) $0$
(c) parallel.
Work Step by Step
(a) Given $\vec v=3i-4j, \vec w=9i-12j$, we have $\vec v\cdot\vec w=3(9)+(-4)(-12)=75$
(b) we can find the angle between the two vectors $\theta=cos^{-1}(\frac{\vec v\cdot\vec w}{||\vec v||||\vec w||})=cos^{-1}(\frac{75}{\sqrt {9+16}\sqrt {81+144}})=0$
(c) the vectors are parallel.
