I am assuming that x = 4 ; y = 550 units ; and price is 8.25
x is the price
y is the demand
"demand varies inversely as the price" - this means that as the price increases, the demand decreases and vice versa.
y = k/x
520 = k / 4
520 * 4 = k
2080 = k
If k = 2080 ; x = 8.25 ; y = ?
y = k / x
y = 2080 / 8.25
y = 252.12
With a price of 8.25, the demand would approximately be 252.