Please solve the answer fully, explaining the working as I$\text{'}$m bit confused at moment.

There are $3500$ vehicles per hour entering an arterial road with three lanes in each direction. The fundamental diagram for this road can be modelled using a triangular flow$-$density relationship, having a total capacity $($maximum flow$)$ of $4500$ vehicles per hour, a critical density of $100$ vehicles per kilometre, and a jam density of $300$ vehicles per kilometre $($for $3$ lanes$).$ Assume that capacity of each lane is identical.

Initially, the arterial carries traffic quite well until a car illegally parks, blocking one of the three lanes and forcing traffic to merge into the other two lanes. A traffic queue quickly builds up behind the parked car.

Assuming that the parked car remains and after a period of $30$ minutes the arrival flow decreases from $3500$ vehicles per hour to $1500$ vehicles per hour.

a$)$ Identify traffic states $($flow and density$)$ on the above arterial road.

b$)$ calculate the shockwave speeds and plot the shockwaves on the fundamental diagram.