the answer is 9
first of all you solve the small brackets, then the bigger brackets, after that you solve the multiplication and division, then finally you solve the addition and subtraction
[ 15 ÷ (7-4) + 2 ] + 6 ÷ 3
[ 15 ÷ (3) + 2 ] + 6 ÷ 3
[ 5 + 2 ] + 6 ÷ 3
[7] + 6 ÷ 3
7 + 2
9