Complementary and substitute commodities in a survey

Question

Question: COMPLEMENTARY AND SUBSTITUTE COMMODITIES In a survey conducted by Home Entertainment magazine, it was determined that the demand equation for VCRs is given by

x = f(p, q) = 10,000 - 10p + 0.2q²

And the demand equation for DVD players is given by

y = g(p, q) = 5000 + 0.8p² - 20q

Where p and q denote the unit prices (in dollars) for the VCRs and DVD players, respectively, and x and y denote the number of VCRs and DVD players demanded per week. Determine whether these two products are substitute, complementary, or neither.