3)

4)

1) 5n-(4m+5n)/n;

5-4m-5n/n;

-4m/n.

2)a^2+b^2+2a*(2a-b)+b*(2a-b)/2a-b;

a^2+b^2+4a^2-2ab+2ab-b^2/2a-b;

a^2+4a^2/2a-b;

5a^2/2a-b.