We are given that there are 2 zombies for every 3 humans.
2 + 3 = 5
To figure the total no. of groups of humans and zombies, we divide the total strength by 5.
85/5 = 17.
Now, to get the total no. zombies and humans, we will multiply 17 by 2 and 3 respectively. The answer is thus 34 zombies and 51 humans.