13 The function fx) models a highway's elevation in relation to sea level. When the function is positive, the highway is above sea level. When the function is negative, the highway is below sea level. Explain how you would determine when the highway was at sea level. 14. Determine the number of degree and the end behaviours of the polynomial y = (x +5)(x - 1)(x +3). Justify your answer. 15 Use polynomial division to show that the general expression for the factors of the difference of two cubes, -y' = (x -y)(x +xy+y" ), is correct