Area of a parallelogram is given by

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The base of parallelogram EFGH is the side FE which is 3 units.
The perpendicular height of parallelogram EFGH is 4 units
Area of EFGH = 3×4=12 units square
The base of parallelogram ABCD is the side AB which is 3 units
The perpendicular height of ABCD is 4 units
Area of ABCD = 3×4=12 units square
Hence, area EFGH equals to area ABCD = 12 units