Purplemath.com is just one source.
Someone also posted that if you go to algebra sites and enter the problem exactly as presented, the answer is 2.
If you change the problem to 48/2(9+3), the answer is 288. If that was indeed the problem, the answer is clearly 288, but that is not the problem.
And if you do use the distributive property, why distribute 2 instead of 48/2?
48/2 is the term that precedes the (9 + 3), isn’t it?