revenue increase. please help me step by step to understand.

3. (10 points) Currently, 1800 people ride a certain commuter train each day and pay $4 for a ticket. The number of people willing to ride the train at price p is q = 600(5 - vp). The railroad would like to increase its revenue Show all of your work. (a) Calculate the elasticity of demand q at price p = 4 (b) Determine whether the demand is elastic or inelastic. (c) Based on your findings, should the price of a ticket be lowered or raised to increase the revenue