Even when you have digits on both sides of the decimal point, adding is done as usual.
3.51 2.33
+ 4.23 + 3.22
-------- --------
7.74 5.55
3.42 1.52
+ 3.25 + 2.34
-------- --------
6.67 3.86
1.33 + 2.22 = 3.55 2.41 + 3.22 = 5.63
2.45 + 2.13 = 4.58 1.09 + 2.10 = 3.19
Now you get to try a few for yourself.