You add/subtract complex numbers simply by adding/subtracting real parts and imaginary parts.
So, the real part of this sum is the sum of the real parts:
[tex]-3+6=3[/tex]
And the imaginary part of this sum is the sum of the imaginary parts:
[tex]5i+2i=7i[/tex]
So, you have
[tex](-3+5i)+(6+2i) = 3+7i[/tex]
