To find the area of a rectangle, you can use the formula:
\[ \text{Area} = \text{length} \times \text{width} \]
In this case, the left side of the poster (which we'll consider as the length) measures 7 units, and the top side (which we'll consider as the width) measures 6 units.
Plugging in the values:
\[ \text{Area} = 7 , \text{units} \times 6 , \text{units} = 42 , \text{square units} \]
Thus, the area of the completed poster is 42 square units.