Answer:
The correct option is 4. The total costs will be the same at 12 months.
Explanation:
The given equations represents the cost of each ISP as a function of t, the duration in months of a service contract.
ISP A:

ISP B:

Equate both the functions to find the time at which the total costs to be the same.

Subtract 10t from both the sides.


Divide both sides by 15.


The total costs will be the same at 12 months. Therefore the correct option is 4.