we have been provided with the information of equation as follow

p = √ (484 – 6x)

market price is set at $20/unit

we put the figure in the equation

p = √ (484 – 6x)
p = √ (484 – 6(20))
p = √ (364)
p = 19.08

market price is set at $20/unit

The demand of the quantity of portable hair dryers is 19.08 hundreds units/week (1,908)