Each Ferris wheel in paradise park has w seats. Each seat in a Ferris wheel can hold x people. How many people can ride y Ferris wheels at the same time?
The number of seats in each Ferris wheel is w. 
The number of people that can ride in each seat is x. 
The number of Ferris wheels is y. 

The number of people that can ride the Ferris wheels at the same time is w*x*y. 

Therefore, w*x*y = 19*15*20 = 5700 people can ride the Ferris wheels at the same time.