3+7+9= 19

19 is greater than 1 1.

Be sure to find a way to exchange the largest number below with any number above, and then try one by one.

4+5+9= 18 3+7+2= 12 is wrong.

2+5+9= 16 3+7+4= 14 is wrong.

2+4+9= 15 3+7+5= 15 that's right.

So switch 9 and 5.