The equation is not set up properly. The 8 should be under the 2, as it is in the ones, while the 1 should be under the 1 as it is 10. The way they set it up tricks you to think that there is a decimal (1.8), when it is really 18.
b)
32.1 + 4.6 = 36.7
32.1
+ 4.6
-----------------
36.7
6 + 1 = 7, so the 1 does not have to be carried as it does not equal 10. In this case it is 0.6 + 0.1 = 0.7, it would have to be 1.0 to carry it to the ones.
