We can tackle this question by simply eliminating the options which are not multiple of 3 or 5. In other words, we have to find the option which can not be the number of goals without assistance.

Option A, we can calculate that 1 goal can be scored without assistance which will get them 3 points. Therefore, 48-3 = 45 which is a multiple of 5.

Option B, 6 goals can be scored without assistance because it means that the team will get 18 points for these goals without assistance. The rest of 30 points can be earned by scoring goals with assistance.

Option C, 11 goals without assistance can earn the team 33 points. Which leaves behind 15 points that can easily be earned by scoring goals with assistance.

Option D, 36 points can be earned by scoring 12 goals without assistance. The other 12 points can not be earned by scoring with assistance. Which means this is right.

Therefore, our answer is D) 12.