Math Help - Finding Cartesian equation of parametric surface.

1. Finding Cartesian equation of parametric surface.

I'm a little confused with this problem.

Find the Cartesian equation of the parametric surface: [2cos(t)cos(s), 3sin(s), sin(t)cos(s)]

Find eqn. of the tangent plane when S = 0, t = pi/2

2. compute x^2,y^2 and z^2

Show

x^2 + 4z^2 = 4cos^2(s)

Then show x^2 + 4z^2 + (4/9)y^2 = 4