I really need help on this simple pre-calculus problem...please!?

Question

Here's the problem:

A company finds that there is a linear relationship between the amount of money that it spends on advertising and the number of units it sells. If it spends no money on advertising, it sells 300 units. For each additional $5000 spent, an additional 20 units are sold.

If x is the amount of money that the company spends on advertising, find a formula for y, the number of units sold as a function of x.

I'm lost. How do I find the formula? Please help!

Answer 1

y=300 + (20/5000)*x = 300 + (2/500)x

Answer 2

Set up the variables and the intercepts. When x=0 (advertising=0) then y=300. Now find the slope, $5000/20 per unit. Simple.