It is known that the number of concert tickets demanded is 150 when the price is $40 and 100 when the price is $60.

1. Find the demand function Q = f(P) and the inverse demand function as P = g(Q).

2. Plot the graph in QP-plane.

3. Use the demand function to find the demand when price (a) increases by $10, (b) decreases by $8.

4. Find the elasticity of demand when the price increases by $10 and interpret the result.