Упростить выражение. (a-3/a^2-3a+9 - 6a-18/a^3+27):5a-15/4a^3+108

( а–3 6а–18 ) 5а–15 ----------------- – ------------ : --------------- = ( а^2–3а+9 а^3+27 ) 4а^3+108 а–3 6(а–3) = ------------------ – ------------------------- : (а^2–3а+9) (а+3)(а^2–3а+9) 5(а–3) : -------------------------- = 4(а+3)(а^2–3а+9 ) (а–3)(а+3)–6(а–3) = -------------------------- : (а+3)(а^2–3а+9) 5(а–3) : --------------------------- = 4(а+3)(а^2–3а+9 ) (а–3)(а+3–6)*4(а+3)(а^2–3а+9) = ---------------------------------------------- = (а+3)(а^2–3а+9)*5(а–3) 4(а–3) = ---------- 5