Primary school mathematics problem, urgent There are two piles of chess pieces, black is three times of white, take five black each time, two white several times, white just finished, black has 13, to process, thank you

Primary school mathematics problem, urgent There are two piles of chess pieces, black is three times of white, take five black each time, two white several times, white just finished, black has 13, to process, thank you

Analysis: take the same number of times, the number of black is three times the number of white
There are: 5 times of black chess + 13 = 3 × (2 times of white chess)
If you take x times, you have
5x+13=2x×3
6x-5x=13
x=13
Then white chess has:
13 × 2 = 26
Black has
26 × 3 = 78

Is the nine digit number composed of 1, 2, 3, 4, 5, 6, 7, 8 and 9 prime or composite? Why?

The nine digits of 1, 2, 3, 4, 5, 6, 7, 8 and 9 are combined
Because 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 = 45 is a multiple of 3
So this nine digit number is also a multiple of 3, so it's a composite number

How many prime numbers can be made up of the nine numbers 1-9? (each number can only be used once)

2,3,5,7,41,89
or
2,3,5,7,61,89
Up to 6 prime numbers can be formed