Please help with this practice question. Show work.

The below table shows the quantity demanded of footballs and volleyballs at a local sports store for different combinations of prices of the 2 goods Price of Price of Quantity Demanded Quantity Demanded Football Volleyballs of Footballs of Volleyballs $20 $15 27 51 $20 $20 29 42 $25 $15 18 57 $25 $20 18 53 When volleyballs are priced at $15, the cross-price elasticity of volleyballs with respect to footballs is , which implies that volleyballs are a (complement or substitute) for footballs