The area of a rectangle is calculated by multiplying its length by its width. In this case, the length and width of the poster are given as:
- Length = 7 units (left side)
- Width = 6 units (top side)
So, the area can be calculated as follows:
\[ \text{Area} = \text{Length} \times \text{Width} = 7 , \text{units} \times 6 , \text{units} = 42 , \text{square units} \]
Therefore, the area of the completed poster is 42 square units.