This worksheet goes well with Unit 4, once students have mastered rhythms and note values. Essentially this is a simple math/addition worksheet, using the note symbols in lieu of numbers.
I ended up having my students complete this worksheet multiple times; the first time they were allowed to use their notes. After a week or so of lots of repetition in class, I weaned the kids off of their notes and had them do the worksheet again.
This worksheet does use some nontraditional/uncommon rhythmic values, like dotted whole notes. While my kids know that they're uncommon, I want them to understand the concept. So this is more than just quarter notes and half notes!