I'm confused. Can you help?

"The community pool charges $8.00 for adults and $5.00 for children. The total revenue for a
particular cloudy day is $648.00. Determine the number of adults and the number of children who
went to the pool that day if twice as many children paid for admission as adults."

1 answer

if there were a adults, there were 2a children, so

8*a + 5*2a = 648
18a = 648
a = 36

36 adults and 72 children