At a movie theater, the size of popcorn bags decreased 20% . if the old bags held 15 cups of popcorn, how much do the new bags hold?

20 percent off of course amp

I’m not absolutely sure but i think it’s 7x6x5x4x3x2=5040 because as the first character you can take any of the 7 given then you are left with 5 then 6 then 4 etc.