Addition is the first few patterns, the middle space, and then several patterns, so add.

About your summer homework? Do it by subtraction. Subtract the sum from the dotted line. That's right.

Why use subtraction? What does the dotted line mean?

Primary school teacher, so I said I should do subtraction as usual. There is such an example in the textbook, and the dotted line is the dividing line of reduction. Some books use small scissors, and some are dotted lines. Of course, if it is a divergent thinking problem, then the answer is not unique, just do what you understand. As long as the child can tell the truth.