Both answers are correct/wrong because the question is ambiguous. Both subtraction and division are non-commutative, which means to ye laymen out there that order matters. 3 - 2 != 2 - 3. 4/2 != 2/4.
We can normally solve this issue by using unit inverses as part of the term, so instead of thinking as 3 - 2, we think of 2 + -1(2) = -1(2) + 2. Equally, for division we can turn 4/2 into 4 * (1/2) = (1/2) * 4. Another approach is polish notation, as previously noted, which is incapable of ambiguity. Operator precedence is a third way of solving the ambiguity, but is somewhat arbitrary and could be easily reversed (it'd just change the 'normal' way of writing things). Finally, braces were introduced as a catch-all ambiguity breaker. Unfortunately, for this expression, none of these were used.
Algebraically, the ambiguity can be expressed by:
48/2(9+3) -> a = 48, b = 2, c = (9+3) = 12,
This gives a/bc, which can be read as both:
a/(bc) = 48 / (2 * 12) = 2 <-- this answer makes more sense algebraically
(a/b)c = (48 / 2) * 12 = 288 <-- this answer makes more sense looking at the numbers, and using the standard taught operator precedence, e.g. BODMAS or equivalent
