smc

Just plug the $x,y$ pair $(6,20)$ into each of the 5 answer choices: (A): $2(6)-4=8\ne 20$ (B): $6^2-3(6)+2=20$ (C): $6^3-3(6^2)+2(6)=120\ne 20$ (D): $6^2-4(6)=12\ne 20$ (E): $6^2-4=32\ne 20$ The only one that works is $\boxed{y=x^2-3x+2}$.