First-grader problem in arithmetic I found this problem in a text book on arithmetic for first graders (7 y.o.) of the former USSR* . The problem comes from the section that covers single-digit addition and subtraction. Here is the screenshot of the problem:



This is the entire problem: there is no textual description accompanying it, and of course no answer at the back of the book. Other problems in the section are of the 1 + 6 = and 8 - 7 = kind, so this should be an elementary problem as well. However, I cannot figure out what is being asked here: I do not remember this notation, because we used different text books.

Can anybody figure out what is being asked by this assignment?


*  A.S.Pchyolko, G.B.Polyak "Arithmetic" Fifth edition. Text book for the first grade of elementary school. Moscow, Printing house of the Department of Education, 1959
Possibly the student is to produce three numbers by adding the number in the centre of the circle to each of the three around it. (Of course by adding $-6$ I mean subtracting $6$, since I assume that the students had not yet been introduced to negative numbers.) I note that the indicated subtractions are all possible in the non-negative integers, a fact that can be viewed as some small evidence in favor of the interpretation.
I notice the first 2 numbers +6 and -6 can be produced by rearranging the given numbers with + and - signs:

2+4 = 6

10 - 9 - 7 = -6

But the last 2 aren't too clear