Hey there! I'm happy to help!
We see that it takes 15 minutes to eat 6 apples. But, we want to find how long it takes to get to sixteen apples. We need to multiply this by something to get our six apples to sixteen. Let's divide 16 by 6 to find what we need to multiply by.
16/6= 2 2/3
So, if we need to multiply our number of apples by 2 2/3 to get to sixteen, we also need to multiply our minutes by 2 2/3.
15(2 2/3)= 40
Therefore, it takes Ritz 40 minutes to eat sixteen apples at this rate.
One trick to solve problems like this fast is to multiply the two different things you see (minutes and apples) and then divide by the other thing you see (apples in this case). Then, you get the minutes.
15(16)=240
240/6=40
I hope that this helps! Have a wonderful day!