Construction of a special region

I have two regions I want to plot, as follows:

1. The base of the solid $S$ is the triangular region (in the $x$-$y$ plane) with vertices $(0,0)$, $(3,0)$, and $(0,2)$. Cross-sections perpendicular to the $y$-axis are semicircles (assuming upward in the $z$-direction).

2. The base of the solid $S$ (in the $x$-$y$ plane) is an elliptical region with boundary curve $9x^2+4y^2=36$. Cross-sections perpendicular to the $x$-axis are isosceles right triangles (assuming upward in the $z$-direction) with hypotenuse in the base.

Is there a way in Mathematica to show students what these regions look like?

ContourPlot3D[(x - (3/2 - (3 y)/4))^2 + z^2 == (3/2 - (3 y)/4)^2,

ContourPlot3D[x^2/4 + (Abs[y] + z)^2/9 == 1, {x, -2, 2}, {y, -3, 3}, {z, 0, 3},