Which of the following is true about the median of a trapezoid?

If f(x)=x^3 and g(x)=2x+7 when g(x)=-5

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

How is working backward similar to solving an equation?