s3-4s2-4s+16=

-12y4/-3y2=

1) 4*s evaluates to 4s

s*3-4*s*2-4*s evaluates to -9s

s*3-4*s*2-4*s+16 evaluates to -9s+16

2) 3*y*2 evaluates to 6y

-12*y*4/-3*y*2 evaluates to -5y