Area the sum of the parallel sides x the perpendicular height

1
Area ½ the sum of the parallel sides x the
perpendicular height A ½(a b)h
Area of trapezium area of parallelogram A ½(a
b)h ?
2
½ah
Area ½ah ½bh ½h(a b) ½(a b)h ?
½bh
Area ½ (8 12) x 9 ½ x 20 x 9
90 cm2
Area ½(7 5) x 6 ½ x 12 x 6
36 cm2
Area ½(3.9 7.1) x 5 ½ x 11 x 5
27.5 cm2