y=-8.50×+135 is slope intercept y=mx+b
You pay a fee to get into the Aquarium, and it's $135 for a four-person family deal. On top of this $135 you might have to pay an extra $5–10 for riding certain rides. That is where the slope can come into the example. Let’s say you go to pet a stingrays, that is $8.50 per activity. So to get into the aquarium with your family is $135, and for every special activity (petting stingrays, taking pictures with dolphins, swimming with sharks, feeling starfish and urchins, etc) you do is going to be $8.50 extra. Don't worry, it's an amazing aquarium so it's worth the cash!
Hope this helps, have a BLESSED and wonderful day! :-)
-Cutiepatutie ☺❀❤