A quadrilateral is a shape with four sides. A trapezoid has one pair of parallel lines and two congruent angles. A parallelogram has opposite sides that are congruent and parallel. A rectangle has two pairs of parallel lines and congruent angles. A rhombus has four equal sides and angles. To find the area of a rectangle, multiply length by width. To find the area of a square, multiply the length of a side by itself. To find the area of a parallelogram, multiply the base by the height. To find the area of a trapezoid, take the average of the top and bottom lengths and multiply by the height.