To find the area of the shaded polygon, let’s follow the suggested method of calculating the area of a rectangle and then subtracting the area of a triangle:

1. Determine the area of the rectangle:

   • The rectangle is 5 units wide and 4 units high.
   • Area of rectangle $= \text{width} \times \text{height} = 5 \times 4 = 20$ square units.

2. Determine the area of the triangle:

   • The triangle has a base of 5 units (the same as the rectangle's width) and a height of 2 units.
   • Area of triangle $= \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times 5 \times 2 = 5$ square units.

3. Calculate the area of the shaded polygon:

   • Area of shaded polygon $= \text{Area of rectangle} - \text{Area of triangle} = 20 - 5 = 15$ square units.

Thus, the area of the shaded polygon is 15 square units.

Would you like further clarification on any step?

Here are five related questions to expand your understanding:

1. How would the area change if the triangle's height increased by one unit?
2. Can this method be applied to other polygon shapes? Why or why not?
3. What other methods could be used to find the area of this polygon?
4. How would the formula change if the shape were split into two triangles instead?
5. Can you determine the perimeter of this shape based on the given grid?

Tip: Breaking down complex shapes into simpler shapes can make area calculations much easier!