Expanding the expressions:

3a - 7 + 4 - a
= 2a - 3

8b - 12 - 2 + 5b
= 13b - 14

Putting both expressions together:

(2a - 3) + (13b - 14)
= 2a + 13b - 3 - 14
= 2a + 13b - 17

So, (3a-7)+(4-a) + (8b-12)-(2-5b) simplifies to 2a + 13b - 17.