In evaluating mathematical expressions you use the following order of priority:
Parenthesis (what is inside them)
Exponents
Multiplication and division (equal priority)
Addition and subtraction (equal priority)
After this narrowing down, if you have terms of equal priority, then you go left to right. So, in this case we evaluate the parenthesis first, resulting in 48/2 × 12. Division and multiplication are equal in priority, so we do the division first, because it is furthest left. That gives us 24 × 12=288.
I have to go on record as saying that while I feel that 288 is the right answer, the syntax of the expression is terrible. It never hurts to put in extra parenthesis or brackets for clarification. I would have expressed this as (48/2) × (9+3).
This question was raised and discussed in the forum of my companion site Wizard of Vegas.