To simplify the expression, combine like terms:

-5/6a + 7/8b + 7/12a - 5/12b

Let's combine the terms with "a" and the terms with "b" separately:

Combining the terms with "a":
-5/6a + 7/12a
= (-5/6 + 7/12)a
To add these fractions, find a common denominator:
= (-10/12 + 7/12)a
= (-3/12)a
= -1/4a

Combining the terms with "b":
7/8b - 5/12b
= (7/8 - 5/12)b
To add these fractions, find a common denominator:
= (21/24 - 10/24)b
= (11/24)b

Therefore, the simplified expression is:
-1/4a + 11/24b