Herons Formula depends on knowing the semiperimeter or half the perimeter of a triangle. All internal angles are of right angle 90 degrees. A quadrilateral has 4 vertices 4 angles and 4 sides.
B 2 12 inches.
Lets consider quadrilaterals which are four sided closed shapes. All internal angles are of right angle 90 degrees. See our trig article for more information or use the formula below. The angle between them is about 120 degrees.