Even when you have digits on both sides of the decimal point, adding is done as usual.
3.512 2.331 + 4.237 + 3.225 -------- -------- 7.749 5.556 3.421 1.522 + 3.254 + 2.342 -------- -------- 6.675 3.864
1.336 + 2.221 = 3.557 2.412 + 3.223 = 5.635
Now you get to try a few for yourself.