The objects in parenthesis serve as any variable would. since we can all agree that it comes to 6/2(3) ,let's replace 2(3) with 2x. Since surely, you cannot simply divide 6 by two and then multiply that by x, you must apply the 2 to the 3, since they are distributed. Two modifies the three, they cannot be separated. In fact, if you really want to go at it, the reason it is 2(1+2) is because the number was really "6/(2+4)" and it was further simplified by taking a two out to become "6/2(1+2)". 2(1+2) are technically the same unit, and therefore must be taken together if you wish to keep it equal to the original, unsimplified version.