Help please

Im trying to evaluate the following, but not sure if i'm going wrong,could someone please check this.

Evaluating 2A+ 3B

Where

To evaluate i use the scalar multiplication?

so:

2Abecomes =

and

3Bbecomes=

So my dillema is, i cant add these together can i because the incorrect rows to columns - or am i thinking this through to much?

Thanks for your help

Ady