TedEd: Can you solve the rebel supplies riddle?

A Ted Ed by Alex Gendler

You are delivering supply boxes to a rebel base in enemy territory. To get past customs, all boxes must follow this rule: If a box has an even number on the bottom, it must have a red top. Someone calls and tells you that 2 of the boxes are marked wrong, but they don’t know which ones. You can see video of them, and two boxes show red and black tops, respectively, and the other two show the bottom numbers 4 and 7. Which boxes do you have to check to make sure the boxes pass customs? You only have to check two. The one with the 4 and the one with the black top. Since the 4 needs to have a red top, you check it; the black box needs to be checked because it can’t have an even number. If it is even, it must be a red top. But don’t we need to check the red box? No, that’s a simple error called the Fallacy of the Converse. This means that just because one condition means another, it does not go the other way. Here, an even number leads to a red box - that doesn’t mean a red box must have an even number. So, you check the black and #7 boxes and save the day.

Bonus: There are four new boxes, except these have labels of food types. Three of them have been mixed up. How many boxes do you have to check to make sure the labels are correct?