Can someone help me on the following questions cos im just so stuck!

1.Find the equations of the tangent and normal to the curve xy=4 at the point where x=2

2.Given that y=ax^2+bx-a^2 has a gradient -4 at (-2,-13), find the possible values for a and b.

3.The radius, r cm of a circle at time 't's is given by r=(t^3)/3 -2t, t >&= 0

Find the rate at which the radius is changing when t=1 and when t=2.

Any help will be much appreciated! Thanks in advance