Question 911012
Drawing a picture would be helpful, as you say.  Using better choices for variables is also a good idea, and in fact very important when using keyboard, computer input and characters.  


Your perimeter definition equation LOOKS like, the left member, P is equal to the right member described as the quantity twenty-one plus the term two times w.  


Use UPPER CASE L instead of the lower case L.
{{{highlight_green(P=2L+2w)}}}.
Much easier to read.


The drawing you want is difficult to code, but maybe a description will help you to make a drawing on paper:
Draw a rectangle.  One pair of opposite sides is 11 meters, and you should label their lengths as such.  The other pair of opposite sides are each L.  Label them.


You want to know L, but only are given P=55 and w=11.  You will see how the data corresponds to your drawing.


{{{55=2L+2*11}}}, according to formula of perimeter and what the given values are.  Solve for L.
-
{{{2L+22=55}}}, combined steps of simple computation and symmetric property of equality;
{{{2L=55-22}}}, equivalent to addition property of equality, using additive inverse of 22;
{{{2L=33}}}, simple computation;
{{{highlight(L=33/2)}}}, Multiplicative Inverse property