Question

Solve P = 2l + 2w for w in terms of P and l.

Answer 1

to solve for w, the way you isolate as follows:

P = 2l + 2w (first move the 2l by changing sign as follows)
P-2l = 2w

Answer 2

now you have

P-2l = 2w (now divide by 2 on both sides) then you have
---- ---
2 2

Answer 3

so P-2l
w = -----
2