A drill string is composed of $6500$ ft of drill pipe $.,ID=4\mathrm{.}778-in.,$ wt$.=21\mathrm{.}9l\frac{b}{f}t)$ and $950$ ft of drill collar $(OD=8-$in$.,ID=2\mathrm{.}5-in.,wt.=154l\frac{b}{f}t$ in $11$ ppg mud. Find the available WOB $($Hint: you need to consider first the drill collar section required to keep drill pipes under tension$).$

WOB$=84847lb$