¼а+³/5а²-¾а²+⅞-⅔а помогите решить

(1/4)a+(3/5)a²-(3/4)a²+7/8-(2/3)a=((1/4)a-(2/3)a)+((3/5)a²-(3/4)a²)+7/8==(3-8)a/12+(12-15)a²/20+7/8=-(5/12)a-(3/20)a²+7/8=(-18a²-50a+105)/120.