Addition
Add the real components of the 2 complex numbers together to get the answers real part. Add the imaginary components of the 2 complex numbers together to get the answers imaginary part. The length and angle of the answer can then be calculated from the origin using basic trig functions.
Subtraction
Subtract the real components of the 2 complex numbers (make sure to get the order correct). Subtract the imaginary components of the 2 complex numbers (make sure to get the order correct). The length and angle of the answer can then be calculated from the origin using basic trig functions.
Multiplication
After calculating the lengths of the two complex numbers, multiply them together. To calculate the angle of the answer add together the two angles formed from the horizontal to those lines whilst rotating anticlockwise.
Division
After calculating the lengths of the two complex numbers, divide one by the other (taking care to get the order correct). To calculate the angle of the answer subtract the two angles formed from the horizontal to those lines whilst rotating anticlockwise (making sure to get the ordering correct.