Answer
$M(k)=r-s$
Work Step by Step
As the total number of group is the sum of the number of males and the number of females, the following is true:
$$T(k)=M(k)+F(k)$$
From this equation:
$$M(k)=T(k)-F(k)$$
Substitute the corresponding values:
$$M(k)=r-s$$
