I do not understand this equation.

Initial values are: PM = $20000 Pc=$1.00 I=$15000 A = $10000 This function is: QT = 200 -.01PT +.005PM-10Pc +.01I +.003A 4.(a). Competition might be a worry for Toyota. PM = the price of Mazadas, Calculate the point Mazada cross-price elasticity of demand with PM = $20000 and Pr = $20000 (which should make QT = 270). Other variables are given at the top before question #1. The formula is: aQT Pm ETM = apm QT (b). Does this elasticity indicate that the demand for Toyotas is relatively responsive to changes in the price of Mazadas? Explain why or why not