The area of a regular polygon is equal to half of the product of its apothem and perimeter.
A = 0.5aP
Find first the perimeter,
P = 5 x (9 mm)
P = 45 mm
Substituting the perimeter and the apothem to the first equation,
A = 0.5(45 mm)(6.2 mm)
A = 139.5 mm²
Therefore, the area of the regular pentagon is equal to 139.5 mm².