Ответ: №4 .
[tex]\dfrac{6a^2b-6a^2}{b+2}\, :\, \dfrac{12a^3}{5b+10}+\dfrac{5}{2a}=\dfrac{6a^2(b-1)}{b+2}\cdot \dfrac{5(b+2)}{12a^3}+\dfrac{5}{2a}=\\\\\\=\dfrac{5(b-1)}{2a}+\dfrac{5}{2a}=\dfrac{5(b-1)+5}{2a}=\dfrac{5b}{2a}=\dfrac{2,5b}{a}[/tex]
