Answer:
3; Sara is driving 30 miles per hour
Explanation:
Here in this question, we want to select which of the options represent what a unit rate is.
When we talk of rate, we are referring to how a particular measured entity is changing in relation to another measured entity. Hence, we are simply looking at how there is a change between two measurable quantities.
Option 1 is not rate, it only tells us Sara ate 1 cookie. How Sara did this, we do not know, whether fast or slow
Option 2 is just measuring distance. We only know that Sara traveled a particular distance. We do not know how fast, or slow this has occurred
Option 3 is our answer. It clearly tells us how the distance Sara is traveling is measured against time
Option 4 is not correct, we only know the number of crackers and apples are, the rate at which this is done, we do not know