Given Arg (- 2 + I) = a, Arg (- 1-3i) = B, find a + B

Given Arg (- 2 + I) = a, Arg (- 1-3i) = B, find a + B

tana=-1/2,tanb=(-3)/(-1)=3
tan(a+b)=(tana+tanb)/(1-tanatanb)=(5/2)/(5/2)=1
a+b=π/4