Question

A firm’s demand function for good x is estimated as follows:-

Qx = 1800 –1/4Px + 1/8Py – 1/3Pz + 1/5Y

Where Qx represents quantity demanded of good x, Px is price of good x, Py is price of good y, Pz is price of good z and Y is income.
Explain whether the law of demand is valid here