Which expression is equivalent?

If f(x)= 3x+6 which of the following is the inverse of f(x)

Mexico city, mexico, is the world's second largest metropolis and is also one of its fastest-growing cities with a projected growth rate of 3.2% per year. its population in 1991 was 20,899,000 people. use the formula p = 20.899e0.032t to predict its population p in millions with t equal to the number of years after 1991. what is the predicted population to the nearest thousand of mexico city for the year 2010?

Can somebody 1. what is the formula for finding the vertical distance between two points on a coordinate plane?