The cost for a party here is the base fee, plus charges for any additional guests.
So we know for a 15-person party, the price is going to be $100. That's a flat (constant) cost.
We know that for each additional person, we add $12. So for [tex]x[/tex] more people, the cost is $[tex]12x[/tex].
Since 100 is constant here, we make that our y-intercept. Even with no additional guests, the cost is still $100.
We add to write [tex]y=12x+100[/tex]. 12 is the constant rate of change (slope).
