y = 12x + 10
Assuming that your question is multiple choice, the variables might be different.
The reason that it's represented as 12x + 10 is because there is a flat fee of $10 when you sign up. From then on afterward, every month you pay $12.
In this equation, the variable 'y' represents the total cost, while 'x' represents the number of months this service was in use.
80/400 as a decimal is 0.2
3 is your greatest
3/3 = 1
18/3 = 6
hope this helps