Grade E drill pipe has the following mechanical performance $395,600lb$ pipe body yield strength. $5"$ OD and $19\mathrm{.}5l\frac{b}{f}t.$ Grade G has $559,800lb$ pipe body yield strength. Determine at what depth you should change from grade E to G using $18$ joints of DC$\text{'}$s $8\mathrm{.}5"$ & $\frac{213}{16}"$ and $11$ ppg mud. Allow for $100,000lb$ overpull on all DP before reaching $80\%$ of body yield $($do not exceed $80\%$ of body yield any time$).$