To obtain a combined resistance of 4Q when a 12Q resistance is present, we need to add another resistance in parallel.

Option 1: This option does not provide the value of the resistance to be placed in parallel, so it is not the correct answer.

Option 2: This option suggests placing a 4Q resistance in parallel with the 12Q resistance. However, this would result in a combined resistance of less than 4Q, so it is not the correct answer.

Option 3: This option suggests placing a 6Q resistance in parallel with the 12Q resistance. Adding these two resistances in parallel would result in a combined resistance of 4Q, which matches the requirement stated in the question. Therefore, option 3 is the correct answer.

Option 4: This option suggests placing an 8Q resistance in parallel with the 12Q resistance. Adding these two resistances in parallel would result in a combined resistance of 3.43Q, which is less than the required 4Q. Therefore, it is not the correct answer.

In conclusion, option 3 is the correct answer as it provides the value of the resistance that must be placed parallel with the 12Q resistance to obtain the desired combined