What type of property is this: -8x=20

What is the average rate of change for this function for the interval from x=2 to x=4 ?

Which of these equations, when solved, gives a different value of x than the other three? a9.1 = -0.2x + 10 b10 = 9.1 + 0.2x c10 – 0.2x = 9.1 d9.1 – 10 = 0.2x

You are at a restaurant and owe $56.20 for your meal. you want to leave an 18% tip. approximately how much is your tip?