In the Compass Appendix 3 I can see how to calculate MOEs for aggregate counts, but not on aggregate percentages, is it done the same way?

Specifically, I am using the S1501 table to look at Educ Attainment. Because there are only 5-year tables for the small area I am looking at, I am looking at 2016 and 2011 tables. The 2011 table only provides percentage estimates - not count estimates (except for the total population) - and percentage MOEs. How can I determine the percent MOE for the aggregate of 2 of those percent estimates? For example, I want to aggregate the estimates/MOEs for "< 9th grade education" and "9-12 grade, no diploma" into one "no HS degree" category.

Very much appreciate any guidance ~

Joanna