You can solve this problem by finding the unit rate first!
If 2 pounds of meat serves 5 that means that 2/5 of a pound serves 1 person.
In ratio form-
1:2/5
The problem is asking how many pounds are needed to serve 13 people, so if you set up a proportion using ratios it would look like this-
1:2/5
13:x
"x" represents the unknown amount of pounds
1 times 13 gets you to 13, so multiply 2/5 by 13 as well.
You should get 5(And)1/5 pounds of meat!