|-56| = -56
|-4| = 4
|15| = 15

First, add the fractions:
2.1/7 + 2.4/7 = 4.5/7

Now, combine the values:
-56 - 4 + 15 + 4.5/7

-56 - 4 = -60
15 - 60 = -45

Therefore, the final answer is -45 + 4.5/7.