It is known that the quantity demanded of a certain make of portable hair dryer is x hundred units/week and the corresponding wholesale price is shown below where p is in dollars.

p = sqrt(225 - 5x)
The supplier will make x hundred units of hair dryers available in the market when the wholesale unit price is what follows (with p in dollars).
p = sqrt(36 + 1.8 x)
Determine the producers' surplus if the wholesale market price is set at $9 per unit.