Define quadrilateral, find parallelogram angles w, x, y given z=98°, and calculate trapezium area given dimensions.

Here are the solutions to the problems:

15. Define the term quadrilateral and state two examples.
A quadrilateral is a polygon with four straight sides and four vertices. Its interior angles sum to $360^\circ$.
Examples: Square, Rectangle.

17. If $z=98^\circ$ find angles $w, x$ and $y$.
Assuming the given quadrilateral is a parallelogram based on the diagram:

Step 1: In a parallelogram, opposite angles are equal.
Given $z = 98^\circ$. Angle $w$ is opposite to $z$.

$$w = z$$ $$w = \boxed{\text{}98^\circ\text{}}$$

Step 2: In a parallelogram, consecutive angles are supplementary (add up to $180^\circ$).
Angle $x$ is consecutive to $z$.

$$x + z = 180^\circ$$ $$x + 98^\circ = 180^\circ$$ $$x = 180^\circ - 98^\circ$$ $$x = \boxed{\text{}82^\circ\text{}}$$

Step 3: Angle $y$ is opposite to $x$.

$$y = x$$ $$y = \boxed{\text{}82^\circ\text{}}$$

18. Calculate the area of the following: