Answer:
Part 7)

Part 8)

Part 9)
Part 10)

Part 11)

Part 12)

Explanation:
Part 7) we know that
The point O is at origin
so its coordinates are

Since the height of the rectangle is h, S and T are h units away from the x-axis
Since the base is b, T and W are b units away from the y-axis
thus the coordinates of the other vertices are

Part 8) we know that
The point O is at origin
so its coordinates are

Since the height of the square is a, S and T are a units away from the x-axis
Since the base is also a, T and W are a units away from the y-axis
thus the coordinates of the other vertices are

Part 9) we know that
Since the square STWZ is centered at the origin and side length is b, S and T are b/2 units away from each axis
The same is true for the other vertices
so

Part 10) we know that
Since the parallelogram has height a, S and T are a units away from the x-axis
The x-coordinate of T and W do not depend on a or b, so use a different variable c for T and W
Thus

In this part another variable for c is acceptable
Part 11) we know that
Since the rhombus STWZ is centered at the origin, the diagonal be on the axes and the diagonals bisect each other, T and Z are t units away from the x-axis, and S and R are r units away from the y-axis
so

Part 12) we know that
Since the the base of the isosceles trapezoid is centered at the origin, S and Z are a units away from the y-axis
The height is c , so T and W are c units away from the x-axis
The distance of T and W from the y-axis, do not depend on a or c, so another variable b is needed
Therefore

In this part another variable for b is acceptable