What is the three$-$week simple moving average forecast for the following numbers?

$\backslash$table$[[$Week$,$Units$],[\backslash$table$[[$Week$],[1]],\backslash$table$[[400],[$units$]]],[\backslash$table$[[$Week$],[2]],\backslash$table$[[800],[$units$]]],[\backslash$table$[[$Week$],[3]],\backslash$table$[[600],[$units$]]]]$

a$.100$ units

b$.600$ units

c$.500$ units

d$.300$ units