For example 3+1 = 4 and it also shows that D = 1+3. It could get confusing if you try and connect the columns with rows and make a double digit sum when you should only focus on one column or row and not mix them up making the wrong result. For example starting from the number 2 in the top row (3+2=A) and add number 1 to the is where one could mess up the puzzle when it should be 3+2 = A only. And that’s how it’s done. Good luck!
