Are you serious?

It's 2.
Basically because when 48÷2(9+3) you do the brackets first. So it's 48÷2(12). But it's only the 2 that is multiplied by 12, not the entire expression. You get 288 when you go 48÷2 is 24 and then x 12 is 288.
If we had x's for example, this is easier to see. 48÷x(9+3), when you solve this it becomes 48÷9x+3x, which is 48÷12x. When x is 2, as in the original equation, 48÷(12x2), the answer is shown to be 2. To get 288 from this, you have expanded 48÷x(9+3) as 48÷x(12), and then solved it by dividing 48 by x and multiplying the whole thing by 12 to get (48÷2)(12), which is absurd. You need to leave the brackets on the 12, and this means the multiplication is done first.You can't just reassign the 12 to be multiplied with the whole thing instead of just the 2.
Further, if you put this on a calculator as 6÷2(1+2) it gives you an answer of 1.