Find the elasticity of demand at the price with the demand of .

This is what i get (285(3)^(1/2))/(9(190)^(1/2)(190/3)^(1/2)) = .5

p= 3

x= (190/3)^(1/2)

dx/dp= (-190)/(9(2x)) and then plug in the x.

What is the correct way how to do this? I know the formula is p/x * dx/dp