A four$-$lane undivided multi$-$lane highway $($two lanes in each direction$)$ has $11-$ft lanes and $5-ft$ shoulders. At one point along the highway there is a $4\%$ upgrade that is $0\mathrm{.}62mi$ long. There are $15$ access points along this grade. The peak$-$hour traffic volume is $2340$ vehicles, with $10\%$ single$-$unit trucks and $10\%$ tractortrailer trucks, and $620$ of these vehicles arrive in the most congested $15-$min period. The posted speed limit is $60m\frac{i}{h}.$ To improve the level of service, the local transportation agency is considering reducing the number of access points by blocking some driveways and rerouting their traffic. How many of the $15$ access points must be blocked to achieve LOS C$?(2$ points$)($Note: Left side clearance for undivided highways is taken as $6ft)$