$12\mathrm{.}1$ A highway cut is being constructed through high$-$mica schist. Drilling tests indicate that air$-$track drills with

$3\mathrm{.}5in.$ STD bits can penetrate at $2f\frac{t}{m}in.$ The drills use $12-ft$ steel. The blasting pattern will be $810$ with $2ft$

of subdrilling. The average depth to finish grade is $12ft.$ What is the drilling time $($no fixed time$)$ required to

penetrate to the required depth?$12\mathrm{.}1$ A highway cut is being constructed through high$-$mica schist. Drilling tests indicate that air$-$track drills with $3\mathrm{.}5$ in$.$ STD bits can penetrate at $2$ ft$/$min$.$ The drills use $12-$ft steel. The blasting pattern will be $8$ x $10$ with $2$ ft of subdrilling. The average depth to finish grade is $12$ ft$.$ What is the drilling time $($no fixed time$)$ required to penetrate to the required depth? ANS $-7\mathrm{.}0$ min Please show work