Please help me with this problem

"A tour bus has 80 seats. Experience shows that when a tour costs $300, all seats on the bus will be sold. For each additional $10 charged, however, 2 fewer seats will be solved. Find a function that represents the revenue derived from a single bus tour."

I couldn't understand the statement actually. It says there are total 80 seats on the bus but for more $10 each time we are producing additional 2 seats meaning the bus has infinite seats I'm quiet dumb please help me at that.

The question is solved in the picture please just explain it.