Answer:
The number of hours.
Step-by-step explanation:
The dependent variable is what you are mesuaring.
Adding rational numbers involves adding decimals and repeating decimals like 4.6666666..... Whole numbers on the other hand involves adding 7+6 which arent exactly decimals
The unit rate is how many calories are in 1 cup of cereal.
Set up a proportion:

Cross multiply and solve:

There are 100 calories per cup of cereal.
To get the calories in 4 cups of cereal, simply multiply the unit rate of 100cals/cup by 4.

There are 400 calories in 4 cups of cereal.
The work is incorrect.
(-6) multiplies both terms inside parentheses. For some reason, the student changed the sign of that multiplier for the second term. The second term of the result should have a positive sign, the result of multiplying (-6)(-2/13) = +12/13.