Let's solve each of these equations step by step:

1) 3(4x + 1) - (12x + 3) + 2a
= 12x + 3 - 12x - 3 + 2a
= 2a

2) x^2 - 2x - 8 + (2x^2 + x - 7)
= x^2 - 2x - 8 + 2x^2 + x - 7
= 3x^2 - x - 15

3) 2x^(3x - x + 1)
= 2x^(2x + 1)
= 2x^(2x) * 2x
= 4x^(2x+1)

4) (3a - 2b)(2a - 5b)
= 3a 2a - 3a 5b - 2b 2a + 2b 5b
= 6a^2 - 15ab - 4ab + 10b^2
= 6a^2 - 19ab + 10b^2

5) (a - 4b)(2a + ab - 2b^2)
= a 2a + a ab - 2a 2b^2 - 4b 2a - 4b ab + 4b 2b^2
= 2a^2 + a^2b - 4ab^2 - 8ab - 4ab^2 + 8b^3
= 2a^2 + a^2b - 8ab^2 - 12ab + 8b^3

I hope this helps! Let me know if you need further assistance.