Wait how do yhu spell apple again?

Which three lengths could be the lengths of the sides of a triangle? 21 cm, 7 cm, 7 cm 9 cm, 15 cm, 22 cm 13 cm, 5 cm, 18 cm 8 cm, 23 cm, 11 cm

Find the roots of the polynomial function f(x) = x^3 + 2x^2 + x

Extra points! find the missing dimension! need asap