The rate Ritz can eat apples is 8/15 apples per minute.
Set the rate (which is measured apples / minutes) equal to 16 apples / t minutes.
(8/15) = (16/t)
Cross multiply.
16*15 = 8t
t = 20
The answer is 30 minutes. You could solve the problem with basic reasoning as well. 16 is twice the number of apples as 8, so the time it takes to eat them will be double 15 minutes.
