The first thing wrong in this video is that the chef thinks that 7x13=28. Even though this is wrong he makes it look like this is the correct answer. One place where he went wrong was when he was writing out the multiplication on the chalk board. Apparently he believes that you can "reuse" numbers so he used the 2 again without the other guy realizing it. the next thing he did wrong was in the addition where he didn't carry the two. If he had carried the 2 he would have gotten 91. Other possible equations would include,

6,12=18

 5,14=25.