How to do this math problem in the third grade of primary school?

Third-grade students can generally answer this question.

Such as the title:

Basketball+Volleyball =58

Volleyball+Football =45

Football+Basketball =77

After observation, it is found that the addition of the left and right sides of the equal sign is equivalent to

Basketball, volleyball, football and twice =58+45+77= 180.

So basketball+volleyball+football = 180÷2=90 (pieces), that is, three kinds of balls ***90.

Basketball: 90-45=45 (pieces)

Volleyball: 90-77= 13 (each)

Football: 90-58=32 (pieces)

I hope you can understand and wish you success! !