There are 27 ways three darts can hit targets because for each dart there are 3 possible targets: 3³=27.
We can produce a score for each of the 27 possibilities:
1+1+1=3, 1+1+2=4, 1+1+4=6,
1+2+1=4, 1+2+2=5, 1+2+4=7,
1+4+1=6, 1+4+2=7, 1+4+4=9,
2+1+1=4, 2+1+2=5, 2+1+4=7,
2+2+1=5, 2+2+2=6, 2+2+4=8,
2+4+1=7, 2+4+2=8, 2+4+4=10,
4+1+1=6, 4+1+2=7, 4+1+4=9,
4+2+1=7, 4+2+2=8, 4+2+4=10,
4+4+1=9, 4+4+2=10, 4+4+4=12.
So we can now write the nine different scores with their frequencies in brackets:
3(1), 4(3), 5(3), 6(4), 7(6), 8(3), 9(3), 10(3), 12(1).
For example, 7(6) means there are 6 ways of getting the score 7.