To begin to solve this problem, we want to find out what ingredients we need to make a single pancake. To do that, we need to use the information already given (what it takes to make 6 pancakes), and divide it by 6.
That means that it takes:
Eggs: 2 ÷ 6 = 1/3
Milk (cups): 1.5 ÷ 6 = 1/4
Pancake Mix (cups): 1/3 ÷ 6 = 1/18
To make 1 pancake.
Now let's look at what it takes to make the number of pancakes with the ingredients we have, 5 eggs, 4 cups of milk (doing the conversion) and 1.5 cups of pancake mix. To find out how many pancakes we can make, we need to know how many times of each ingredient of the unit recipe is in this recipe.
We get:
Eggs: 5 ÷ (1/3) = 15
Milk: 4 ÷ (1/4) = 16
Mix: 1.5 ÷ (1/18) = 27
Looking at these, we take the smallest of these numbers (because we can't have any partial pancakes). That means that we can make 15 pancakes with what's provided to us.