Here is a comment from Prof. Ed Lazowska (Bill & Melinda Gates Chair at UW CSE) in a Quora article:
“At the University of Washington we have two degree programs: a B.S. in Computer Science offered through the College of Arts & Sciences, and a B.S. in Computer Engineering offered through the College of Engineering. … It tends to be easier to dual-major from Computer Science, because there is heavy overlap in the distribution requirements with other A&S programs - we have lots of dual majors with music, art, math, biology, linguistics, [etc.].”
Thus, it seems possible for CS majors to add other majors and minors (and degrees) from within the College of Arts & Sciences.
It looks like combining a B.S. in CS and a B.A. in Business Adminstration would be considered a “double degree” as opposed to a “double major” and would entail certain credit requirements. See:
https://www.washington.edu/uaa/advising/academic-planning/majors-and-minors/overview/
Perhaps contact the CS or Foster School of Business advising staff to inquire whether this combination of degrees is possible at the UW.