If we try to look at the item c. we can say that the summed up value for 0.25x, 2y, and 55 is the total cost for the family plan.
a. 0.25
Since in item c. 0.25 is multiplied to x and in the item it is stated that there is an additional usage cost per x number of cellphone above the plan amount, this means that the charge for every cellphone not initially included in the plan is equal to 0.25
b. 2y
From the given, it is stated that there is an additional charge if y megabytes of data is used above the plan amount. Hence, 2 is the charge per megabyte of data
c. As mentioned in the earlier part of this answer, the expression is the total cost or charge for the smartphone family plan which already includes the base pay.
