2) (-3 7/15) + (-0.4) + (-6 1/3)

First, convert all mixed numbers to improper fractions:
-3 7/15 = -3 15 + 7 = -45 + 7 = -38/15
-6 1/3 = -6 3 + 1 = -18 + 1 = -17/3

Now, add:
-38/15 + (-0.4) + (-17/3) =
-38/15 - 4/10 - 17/3 =
-38/15 - 6/15 - 85/15 =
(-38 - 6 - 85) / 15 =
-129 / 15 =
-8 9/15 =
-8 3/5

Therefore, the result is -8 3/5.

4) (-2 5/8) + (-9.25) + (-3/4)

First, convert all mixed numbers to improper fractions:
-2 5/8 = -2 * 8 + 5 = -16 + 5 = -11/8

Now, add:
-11/8 + (-9.25) + (-3/4) =
-11/8 - 37/4 - 3/4 =
-11/8 - 37/4 - 3/4 =
(-11 4 - 37 2 - 3) / 8 =
(-44 - 74 - 3) / 8 =
-121 / 8 =
-15 1/8

Therefore, the result is -15 1/8.