$($total$\_$surface$\_$area $=2*($length $+$ width$)*$ height # Total surface area of all four walls$)$

$-$ Why is the number $2$ at the beginning? And is it multiplying what is it the parentheses or the whole formula?

total$\_$surface$\_$area $=2*($length $+$ width$)*$ height # Total surface area of all four walls

$-$ can I get a break down of this formula? thanks