Price Elasticity of Demand

The question is below:

Given a demand function QD = 17 – 6P, find the elasticity of demand at P = \$2. Is the demand elastic or inelastic when P = 2?

Heres what I know: Q = 17 - 6 (2) = 5

δQ/δP = -6

But how do I find εD?

I figured it out. In my solution: $$\epsilon_D = \partial Q / \partial P \cdot P/ Q = -6 * (2/5)$$