A flexible pavement was designed to have a $4-$inch sand$-$mix asphalt surface, $8-$inch

soil$-$cement base, and a $10-$inch crush$-$stone subbase. All drainage coefficients were $1\mathrm{.}0.$

The pavement was designed for $80012-$kip single axles and $1,60034-$kip tandem axles

per day in the design direction. The design parameters were reliability $=95\%,$ overall

standard deviation of traffic $=0\mathrm{.}35,$ initial PSI $=4\mathrm{.}7,$TSI$=2\mathrm{.}5,$ and the soil resilient

modulus $=2582l\frac{b}{i}{n}^2.$ If the road has four lanes in the design direction $($and was

conservatively designed$),$ how many years was the pavement designed to last? Use

Python or Excel to solve $W_{18}.$