The problem is 48 divided by 2(9+3); it is not 48 divided by 2 and then that result being multiplied by 12.
The numerator is 48 and the denominator is 2(9+3)n or 24.
Write it down on a piece of paper and your will see the answer is 2.
You are simply wrong. The division operator does not automatically make everything to its right part of the denominator.
What is 9 / 3 * 3?