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

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$.5$

b$.20$

c$.0$

d$.40$