The derivative of is -35, and you don't need the derivative of ;
The price elasticity is given by
and the demand equation is given by
and p is given as 4 for
So i plus in 4. Which gives q as 560.
Then i take derivative of q which is 35? and derivative of p which is one?
Then throw them in the elasticity equation and get -0.25.
Does that make sense?