I have a couple of questions on centroids. If anybody could help me out, that would be great.

Find the centroid of the region bound by y=2x y=4 y-axis. What is the centroid (ordered pair)?

Find the centroid of the region bound by y=(36x)-(x^2) y=x. What is the centroid (ordered pair)? For the x-coordinate, I got (137/2). Is this right?

Find the centroid bounded by y=4x x=4 x-axis. What is the centroid (ordered pair)? I got the coordinates (2/3 , 8/3). This is apparently wrong as well.

I have been working on these for awhile, and I need some help. If you can show me how to set up the integrations, I can finish it from there. All help is appreciated, I am plum stuck!