For more extensive instructions, check out How to Find the Area of a Quadrilateral
This works because a square is simply a special rectangle that has equal width and length. So, in solving k=b*h, b and h are both the same value. So, you end up squaring a single number in order to find the area.
If the side opposite to the base is not long enough that the perpendicular line crosses it, extend the side along the line until it intersects the perpendicular line.
For more extensive instructions, check out How to Find the Area of a Parallelogram
For more extensive instructions, check out How to Calculate the Area of a Trapezoid
For more extensive instructions, check out How to Calculate the Area of a Triangle
For more extensive instructions, check out How to Find the Area of Regular Polygons
For more extensive instructions, check out How to Calculate the Area of a Circle
For more extensive instructions, check out How to Find the Surface Area of Cylinders
