Answer:
Step-by-step explanation:

Letter A is a correct way because $9 * gigabyte = total cost (28.50)
Letter C is a correct way, It is the same as Letter A except they use an 'x' for multiplication.
Letter D is correct because 28.50/the cost of additional gigabytes($9) gives the amount of the gigabytes used.
Letter B is incorrect.
Centralizándolos situationist beneficioso punto
Answer:
Below.
Step-by-step explanation:
A linear function contains a variable of the first degree only - for example f(x) = 2x - 1 or f(z) = 3z.
So y = x + 5 is linear.
The awnser is either 1050 or 3000 choose witch one is more reasonable for your question