explain how to get the other variables in the expression besides b

Determine the product terms for the Karnaugh map in Figure 4-35 and write the result- ing minimum SOP expression. B FIGURE 4-35 Solution Eliminate variables that are in a grouping in both complemented and uncomplemented forms. In Figure 435, the product term for the 8-cell group is B because the cells within that group contain both A and A, C and C, and D and D, which are eliminated. The 4-cell group contains B, B, D, and D, leaving the variables A and C, which form the product term AC. The 2-cell group contains B and B, leaving variables A, C, and D which form the product term ACD. Notice how overlapping is used to maximize the size of the groups. The resulting minimum SOP expression is the sum of these product terms: B+AC+ ACD