Given the following costs and activities for Falcon Company electrical costs, use the high$-$low method to calculate Falcon' variable electrical costs per machine hour.

$\backslash$table$[[,$Costs,Machine Hours$],[$April$,$$$4,600,15,000],[$May$,3,700,10,000],[$June$,5,300,18,000]]$

a$.$ $$0\mathrm{.}67$ per unit

b$.$ $$0\mathrm{.}36$ per unit

c$.$ $$0\mathrm{.}20$ per unit

d$.$ $$20\mathrm{.}00$ per unit