A $6-$lane divided highway is on a rolling terrain with only two access points per mile. The highway has $10-$ ft lanes, with a $5-$ft shoulder on the right side and a $3-$ft shoulder on the left side. The peak$-$hour factor is $0\mathrm{.}90.$ The directional peak$-$hour volume is $3,000$ vehicles per hour. There are $6\%$ large trucks, $2\%$ buses, and $2\%$ recreational vehicles. Population adjustment factor is $0\mathrm{.}95).$ Base free$-$flow speed is $60$ mph$.$

a$)$ Determine the current level of service.

b$)$ A local supply store is to open a factory near this highway. How many large trucks can be added to the peak$-$hour directional volume before LOS becomes E$?$