To solve, keep filling in the missing information until you get the number you want: the total "Yes" for band.
In the bottom row, the number of students in the chorus is 15 and the total number of students is 32, so the number of students NOT in chorus is 32 - 15 = 17. Write that number in the blank in the bottom row.
Now the chorus' "No" column has a total of 17, which is the sum of 5 and a blank. So the value of the blank must be 17 - 5 = 12, and there are 12 students who are in the band but not in the chorus.
Now you can find the total number of students in the band. There are 6 students who are in both the band and the chorus, and there are 12 students who are in the band but not in the chorus, so the total number of students in the band is 6 + 12 = 18.
