Help my sister with this study island

n= +9; D

Step-by-step explanation:

(12x^5 + 6x^3 +x) - (x+26)(2nx^2+1)

2x9= 18; now let's see how n=9 works out :

12x^5 + 6x^3 +x - (18x^3+468x^2+26+x)

= Distribute the negative: 12x^5+6x^3+x-18x^3-468x^2-26-x

= Now cross cancel: 12x^5+6x^3-18x^3-468x^2-26

= Add/substract: 12x^5-12x^3-468x^2-26

n= +9 does work, thus we get the simplified 12x^5-12x^3-468x^2-26

A.

Step-by-step explanation:

85/100 = 85%