[(12-4)•2+11]/3

Work with the innermost set of parenthese first:

[ (8) * 2 + 11 ] / 3

Finish inside the set of brackets, doing multiplication before addition:

[ 8 * 2 + 11 ] / 3

[ 16 + 11 ] / 3

[ 27 ] / 3

Now finish by dividing 3 into 27.