You are given the data below:

${\displaystyle \underset{?}{\overset{?}{}}}x=20$;${\displaystyle \underset{?}{\overset{?}{}}}Y=3,500$;${\displaystyle \underset{?}{\overset{?}{}}}xY=20,000$;${\displaystyle \underset{?}{\overset{?}{}}}{x}^2=325,Y^2=475,000$;$N=4$

Estimate the variable cost per unit using the regression analysis method.

a$.$ $$11\mathrm{.}12$

b$.$ $$11\mathrm{.}11$

c$.$ $$11\mathrm{.}01$

d$.$ $$12\mathrm{.}11$