A route connects an origin$-$destination pair with a performance function $t_1=8+x_1$ and another with $t_2=3+x_2($with $x\text{'}$s in thousands of vehicles per hour and $t\text{'}$s in minutes$).$ If the total origin$-$destination flow is $4000ve\frac{h}{h},$ determine route travel times, total travel time $($invehicle minutes$),$ and route flows for each of the four traffic assignments

a$)$ All or nothing

b$)$ Incremental

c$)$ user equilibrium

d$)$ system$-$optimal