Chapter 2 - Set Theory - 2.4 Set Operations and Venn Diagrams with Three Sets - Exercise Set 2.4 - Page 94: 100

$VI$

"White Christmas" was recorded by Bing Crosby, a solo artist. It sold 50 million and was released in 1942. Thus, this song belongs to the sets "Sales exceeded 15 million" and "Recorded before 1990" but not to "Recorded by a group." Thus, it must be written in Region $VI$.