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 (which we can consider as the width) measures 7 units, and the top side (which we can consider as the length) measures 6 units.
So, the area of the poster would be:
\[ \text{Area} = 7 \times 6 = 42 \text{ square units} \]
Therefore, the area of the completed poster is 42 square units.