Problem-solving exercises:

(a) Use the arc-approximation formula to calculate the price elasticity of demand coefficient of a firm's product demand between the (quantity, price) points of (10, $20) and (14, $16).

(b) Calculate the cross-price elasticity of demand coefficient of a firm's product X, given that a 10% increase in the price of its close substitute, product Y, causes the quantity demand of product X to increase by 8%.

(c) Calculate the income-elasticity of demand coefficient for a product for which a 5% increase in consumers' income will increase the quantity demanded by 6%.