Answer
$\approx 132^0$
Work Step by Step
Sum of two vectors can be written as
$\overrightarrow {r}=\overrightarrow {a}+\overrightarrow {b}$
$r=(a_{x}\widehat {i}+a_{y}\widehat {j}+a_{z}\widehat {k})+(b_{x}\widehat {i}+b_y\widehat {j}+b_{z}\widehat {k})
=\left( a_x+b_x\right) \widehat {i}+\left( a_y+b_y\right) \widehat {j}+\left( a_{z}+b_{z}\right) \widehat {k}=\left( 4.0m+\left( -13.0m\right) \right) \widehat {i}+\left( 3.0m+7.0m\right) \widehat {j}=-9.0m\widehat {i}+10.0m\widehat {j}$
Then the angle of this vector can be calculated using,
$\tan \theta =\dfrac {r_y}{r_x}=\dfrac {10.0m}{-9.0m}=-\dfrac {10}{9}\Rightarrow \theta =\tan ^{-1}\left( -\dfrac {10}{9}\right) \approx 132^0$
