Polynomial problem

I am needing a little help to solve a few problems and also learn how to do this without pulling the rest of my hair out and also begin to have a better understanding I will post four questions that need assistance and I will be forever in your debt. I would like to also give back in return some way. Here is my problem;
a. Suppose a market research company finds that at a price of p = $420, they would sell x = 16 bicycles each month. If they lower the price to p = $390, then more people would purchase the bicycles, and they can expect to sell x = 22 bicycles in a month’s time. Find the equation of the line for the demand equation. Write your answer in the form p = mx + b. Hint: Write an equation using two points in the form (x,p).

You have two coordinate points:

(16,420) and (22,390)

Use these two points to find the line equation.

First, find the slope, m.

\(\displaystyle m=\frac{420-390}{16-22}\)

Then, along with m, sub either point into y=mx+b and solve for b. You're done.

Let me know what you get.

The slope is going to be negative. Why?.

m=-5

I am not sure why it would be -5 ?

Because x is the number of bikes sold, and y is the price in dollars.

The higher the price, the less bikes sold.