(ab+b^2)/3 : b^3/3a + (a+b)/b Please! T_T

[latex]\displaystyle \frac{ab+b^2}{3}:\frac{b^3}{3a}+\frac{a+b}{b}=\frac{3ab(a+b)}{3b^3}+\frac{a+b}{b}= \\ \\ \frac{a(a+b)}{b^2}+\frac{a+b}{b}=\frac{a(a+b)}{b^2}+\frac{b(a+b)}{b^2}=\frac{(a+b)(a+b)}{b^2}= \\ \\ \frac{(a+b)^2}{b^2}=\left(\frac{a+b}{b}\right)^2=\left(\frac{a}{b}+1\right)^2[/latex]