Verified answer

1) 3a^3×1/3a^3×4a^3 b^5+2a^2 b^3×1/2a^2 b^3×6a^4 b^2+

+4b×1/4b^4×3a^6 b

3a^3/12a^6 b^5+2a^2 b^3/12a^6 b^5+4b^4/12a^6 b^5

3a^3+2a^2 b^3+4b^4/12a^6 b^5

2) 25a^3+8+90a^4/10a^6

90a^4+25a^3+8/10a^6

3)acb/acac+cb/ca^2c+ab/a×ac^2

abc/a^2c^2+bc/a^2c^2+ab/a^2c^2

abc+bc+ab/a^2c^2

4) 2(a+b)+2(a-b)/(a-b)×(a+b)

2a+2b+2a-2b/a^2-b^2

4a/a^2-b^2