the agrument of any complex number is defined as its angle.
if a complex number be Z=a+ib then the agrument of Z is given by,
Agr|Z|=A
where, tanA=b/a i.e. A=tan^-1(b/a)
by the question,
a=-4 and b=4
so A= tan^-1(4/-4)= tan^-1(-1)=135°
therefore the agrument of -4+4i is 135°
