$\backslash$table$[[\backslash$table$[[$To$],[$From$]],\backslash$table$[[$Coal$],[$Valley$]],$Coaltown,$\backslash$table$[[$Coal$],[$Junction$]],$Coalsburg,Supply$],[$Morgantown$,,50,,30,,60,,70],[30,,5,,,,,,35],[$Youngstown$,,20,,80,,10,,90,60],[,,40,,20,,,],[\backslash$table$[[$Pittsburgh$],[$Demand$]],,100,,40,,80,,30,\backslash$table$[[25],[120]]],[,,,,5,,20,],[30,,45,,25,,20,]]$

If the best improvement index is $-110$ from Pittsburgh to Coaltown. What is the Filling quantity for this cell and modifying those cells on the stepping stone path?

a$.20$

b$.0$

c$.40$

d$.5$