Answer
(a) $140m, 59^{\circ}\space south\space of \space east.$
(b) displacement remains the same.
Work Step by Step
(a) We can find the required magnitude and direction as follows:
$\vec A+\vec B=(-72m)\hat x+(120m)\hat y$
We obtain the displacement in the reverse direction as
$-(\vec A+\vec B)=(72m)\hat x+(-120m)\hat y$
Now the magnitude is given as
$|-(A+B)|=\sqrt{(72)^+(120)^2}=140m$
and direction is
$\theta=tan^{-1}(\frac{120}{72})=59^{\circ}$ south of east
(b) We know that the outcome of vector addition doesn't depend on the order of addition. Hence, the displacement remains the same.
