Answer
2, 6, 12, 12.
Work Step by Step
The lower two frequencies are the same as the first two frequencies, so they are 2 and 6. Now we have to find the rest two frequencies, which we can assume are peak frequencies. This can simply be done by subtracting the sum of the frequencies we know (2+6+6+2=16) from the total (40) and dividing it by two. Therefore the peak frequency is 40-16=24, 24/2=12, therefore the two peaks are 12.
