What property is being shown?

-6g + 10 + g = -6g + 10 + 1g

Tom wants to order tickets online so that he and three of his friends can go to a water park the cost of the tickets is 16.00 per person there is also a 2.50 one-time service fee for ordering tickets online write an expression in term of n that represents the cost for n ordering tickets online

How to do this , and can some one explain

Is the ordered pair (-10, 7) a solution to the equation y = 17 – x? yes or no