A Formula Is Given, Along with Values for All but One

A formula is given, along with values for all but one of the variables in the formula. Find the value of the variable that is not given.
- $P=2 L+2 W ; L=6, W=3$

A) $\mathrm{P}=9$
B) $P=18$
C) $P=36$
D) $\mathrm{L}=18$