We are told that the probability that a randomly chosen teacher is female is 3/5, or 60%.
This means that the overall proportion of female teachers at this school is also 3/5, or 60%.
In turn, this means that the overall proportion of male teachers at this school is 1 - 3/5 = 2/5.
Knowing that the total number of male teachers at the school is 36, and that their overall proportion is 2/5, we can easily solve for the total number of teachers at the school.
Let x denote the total number of teachers at the school.
3/5 * x = 36
x = 36 * 5/3
x = 60.