Using the high$-$low method, calculate variable utilities costs per machine hour.

$\backslash$table$[[,$Cost,Machine Hours$],[$January$,$$$8,100,13,900],[$February$,14,500,20,500],[$March$,7,500,10,500],[$April$,9,200,18,900]]$

a$.$ $$0\mathrm{.}50$

b$.$ $$0\mathrm{.}25$

c$.$ $$0\mathrm{.}70$

d$.$ $$0\mathrm{.}63$