Why didn't some materials Sink in water and some others didn't?​

Items that are denser than water sink and items that are less dense than water float

This is a problem for 2 equations and 2 unknown.
so let x be the number of adults in the breakfast
y be the number of children present in the breakfast

so the total people attended is 500, in equation form
x + y = 500

and the total sales made by disney is $ 7355, in equation
17.95x + 12.95y = 7355

so we can solve the equation simultaneously so solve for the values of x and y

so the number of adults at the breakfast x = 176 adults and y = 324 children