Verified answer

y=(x-8)^2(x-5)+4,

y'=2(x-8)+(x-8)^2,

2(x-8)+(x-8)^2=0,

(x-8)(3x-18)=0,

x-8=0, x_1=8,

3x-18=0, x=6,

f(6)=8,

f(8)=0,

f(20)=2164,

min y = 0, x=8