Building EXIT signs are being sold. At a price of $19.75 per sign, 42 signs can be sold and at a price of $48.15 per sign, 33 signs can be sold. Assuming linear demand, what is the price that should be charged, to the nearest penny, if 6 signs are to be sold?

You have two sets of data points: (19.75,42) and (48.15,33)

Now, use those points to find the line equation. Then, plug in x=6.