the area of a rectangle is simply width * length,
well, you have both, so is just their product
[tex]\bf \stackrel{width}{\cfrac{3}{7}}\cdot \stackrel{length}{\cfrac{2}{9}}\implies \cfrac{3\cdot 2}{7\cdot 9}\implies \cfrac{1\cdot 2}{7\cdot 3}\implies \cfrac{2}{21}[/tex]
