Please answer it correctly this is for my mining engineering class assignment. Thank you

A horizontal coal seam is mined with a systematic room and pillar mining method.

Rectangular pillars $25-$ft$-$wide and $45-$ft$-$long are employed. The entry width is $20$ feet in

both directions. The mining height is $5$ feet. The average specific gravity of the

overburden is $2\mathrm{.}50.$ The coal seam is located $1000ft$ below the ground surface.

Determine the extraction ratio and the average pillar stress.

The average in$-$situ strength of coal is generally $900$ psi for a $3-$foot coal cube with a

$\frac{w}{h}$ ratio of $1.$ Use the Mark$-$Bieniawski formula to estimate the strength of these

coal pillars.

What is the safety factor for the coal pillars and is it adequate?