Q$6[6$ pt$]$ In Figure $4\mathrm{.}6,$ the sum of the four cells for class $1$ is $367.$ So is it for class $2$ and $3.$ In this figure, it is assumed that each email must be classified into one and only one of the three classes $($urgent$,$ normal, spam$).$ Now imagine the labels become $\{$sports$,$ education, politics$\},$ and each email can be classified with zero, one or more labels. For example, it can be about both sports and education. In this case, we sometimes call the email is associated with a label.