The demand function for a certain item is $$Q = p^{2}e^{-(p+7)}$$

$p$ represents the price of an item and $Q$ represents the number of items sold at that price.

Use interval notation to indicate the range of prices where the demand elasticity is regarded as elastic or inelastic. (Help with interval notation. )

Here, "demand elasticity" is the absolute value of $\displaystyle \frac{\text{percent change in quantity}}{\text{percent change in price}}$ for an infinitesimal change in price, so $$E = \left| \lim_{\Delta p \to 0} \frac{ \Delta Q / Q}{\Delta p / p} \right| \ .$$

a) The range of prices for elastic demand is

b) The range of prices for inelastic demand is

c) The price for unitary elasticity is