The Rotterdam model can be used to estimate one form of this quantity, for which Richard Stone was the first to empirically derive a linear expenditure system. For a firm in a perfectly competitive market, this quantity is infinitely elastic. The Slutsky equation (-5[1])relates the Marshallian form of this quantity to its Hicksian form by accounting for the substitution and income effects. (10[1])The cross elasticity of this quantity (10[1])measures its sensitivity (-5[1])to changes in a different good’s price. For Veblen goods, this quantity (10[1])[emphasize] (10[1])increases as price increases, often due to (10[1])the value of those goods as status (10[1])symbols. For 10 points, what quantity is defined as consumers’ willingness and ability to buy a certain (10[1])good? (10[1])■END■