How to solve...

Topic $3-$ Transportation D$...$

There are three possible routes that a driver can take to go Zone $1$ to Zone $2.$ The link performance functions of these two routes are:

$t_A=30+2Q_A$

$t_B=21+3Q_B$

$t_C=18+6Q_C$

where $t$ is in minutes and $Q$ is in ${10}^3$ veh$/$h

Given that $t_A=t_B=t_C$ and $Q_A+Q_B+Q_C=6\mathrm{.}5$

Determine $Q_A($in veh$/$h$).$

No unit is required for your answer and leave your answer in the nearest whole number.

Note: $Q$ is in ${10}^3$ veh $\frac{?}{h}$