You simply have to sum corresponding coordinates with each other.
Vector A is (3,2,0), meaning that its i-coordinate is 3, its j-coordinate is 2, and it has no k coordinate (it's zero).
Similarly, vector B is (0,1,2), meaning that its i-coordinate is 0, its j-coordinate is 1, and its k-coordinate is 2.
So, the sum of the i-coordinates is 3+0=3
The sum of the j-coordinates is 2+1=3
The sum of the k-coordinates is 0+2=2
So, the sum vector is A+B=(3,3,2)=3i+3j+2k.
For A-B, you can work in the exact same way, but you'll subtract the coordinates instead of adding them.
