Final answer:
The $2.25 for a large Finito is a unit rate, as it represents the cost for one unit. Proportional reasoning helps calculate the total cost for a family by multiplying this unit rate by the number of family members.
Step-by-step explanation:
When it's stated that a large Finito costs about $2.25, this amount is considered a unit rate because it represents the cost of one unit, in this case, a single Finito. Using proportional reasoning to find the total cost for a family requires you to multiply the unit rate by the number of family members. For example, if you have 4 family members, the total cost would be 4 times $2.25. This concept is similar to finding out how much one would spend on groceries or postage by multiplying the quantity by the price per unit.