The largest printed area of the poster would be when the width and height of the poster are equal. To find the width of the poster, we need to subtract the total area of the margins from the total area of the poster.
The total area of the margins is 6 cm x 4 cm + 4 cm x 6 cm = 88 cm2.
Therefore, 245 cm2 - 88 cm2 = 157 cm2.
We can then use the formula A = W x H, where A is the area and W and H are the width and height of the poster, respectively.
Therefore, 157 cm2 = W x W.
We can solve for W by taking the square root of both sides.
Therefore, W = √157 = 12.5 cm.
Therefore, the width of the poster should be 12.5 cm in order to have the largest printed area.