6b^3+48b/b^3+64-3b^2/b^2-4b+16
=(6b^3+48b)/(b +4)(b²-4b+16) -3b²/(b²-4b+16) = =(6b^3+48b -3b²(b+4)) /(b+4)(b²-4b+16) = =(6b^3+48b -3b^3 -12b²) /(b+4)(b²-4b+16) = =(3b^3 +48b -12b²) /(b+4)(b²-4b+16) = =3b(b² -4b+16) /(b+4)(b²-4b+16) = =3b /(b +4)